1. Issues subordinate to the existence or exercise of jurisdiction
If there is dispute whether the parties did make an agreement at all, it is widely held that for the purposes of jurisdiction, attention has to be confined to whether they agreed or failed to agree to the jurisdiction of a court, and that this failure cannot be demonstrated by merely showing that they failed to reach agreement on the terms of a substantive contract, or by showing that they did reach agreement, but that one of the parties has since rescinded the substantive contract (for example, see art 25 final sentence Brussels I Regulation (recast)). Several overlapping reasons explain why this should be so. Not all legal systems take the view that an agreement for the jurisdiction of a court requires it to be shown that there was a contractually binding agreement to that effect: a unilateral statement of willingness to accept the jurisdiction of a court, or to renounce the jurisdiction of another court, ought to be capable of being effective, quite apart from any substantive contract. Moreover, the parties might well have intended that the designated court should have the particular function of being the body which will determine whether the parties were contractually bound to each other; it would defeat the rational intentions of the parties to argue that the jurisdiction of the court could only ever be agreed to where the parties had made a valid and binding contract which contained this provision as one of its terms and which remained in force. Whether achieved by a principle of severability or by regarding an agreement on jurisdiction as something separate and distinct from a contractual agreement on jurisdiction, the end result should be the same: to impeach the substantive agreement is not to impeach the jurisdictional agreement associated with it; the arguments which impeach an agreement on jurisdiction will generally have to be specific to the jurisdiction agreement.
But if there is a dispute as to the jurisdictional agreement, a court must take a practical approach to the question whether there is an agreement on jurisdiction to which it may be asked to give effect. The procedural law of most jurisdictions will, it seems, resolve this question by asking which side has the better of the argument at the point at which the jurisdictional decision needs to be taken. In spite of what is now said in art 31(2) Brussels I Regulation (recast), there is no a priori reason to prefer the contentions of the party who contends that there was or is an agreement on the jurisdiction of the court over those of the party who denies this. No doubt a court should be astute to frustrate a party who, having agreed to the jurisdiction of a court, now repents of his choice and seeks to find reasons, which may be genuine or spurious, but which might require lengthy investigation to get to their root, to prevent its having effect. It may also be that if the parties have brought or allowed themselves to come to the point at which a court could properly conclude that there was an agreement on jurisdiction, the proposed agreement on jurisdiction should be given the benefit of the doubt. But this does still involve taking sides, even if conditionally, with the litigant who contends that there was an agreement on jurisdiction, and this may be open to question.
There is no reason to suppose that an agreement to the jurisdiction of a court needs to be made in contractual form: there is every reason to suppose that it does not need to be, though if it is contained in a contract, it may have other effects or additional consequences as a result. It should be open to a party to prorogate jurisdiction by a unilateral act as well as by contractual agreement, and if jurisdiction may be prorogated by voluntary appearance, it should also be possible to assent to it by unilateral declaration. The tradition of the common law has been rather slow to acknowledge that this is possible, for most of its thinking about jurisdiction agreements has taken place in the context of contractual disputes in which the alleged jurisdiction agreement is, if it exists at all, a contractual term. But it should neither be accepted nor deduced that this places any limits on the manner in which the agreement is arrived at or on the circumstances in which the assent of the defendant to the jurisdiction may be shown. For example, for C to be bound by a jurisdiction agreement entered into between A and B, C may be substituted for B as a contracting party by process of law, but if this does not happen, C must manifest his own jurisdictional consent, in proper form: this requires no contract to be made by C, but does require some form of formal, unilateral act. Brussels I Regulation (recast), in this respect following the approach of the Hague Choice of Court Convention (→Hague Conference on private international law), says that the validity of the agreement on jurisdiction is to be assessed, where there is dispute on the matter, by recourse to the law of the designated court (art 25(1) Brussels I Regulation (recast)). Though this is consistent with the view that the agreement on jurisdiction does not need to be, or subjected to scrutiny as though it were, contractual, for the law of the designated court might not be the law of the substantive agreement between the parties, it will still add unnecessary complexity to the law. Of course, if the parties have made a contractual agreement as to where litigation will or will not take place, then while this cannot override or suppress the jurisdictional rules of the court whose jurisdiction is otherwise in dispute, it may lay the foundation for a separate argument about the failure to comply with contractual promises, and which is examined further below.
However, even if an agreement on jurisdiction need not be contractually valid or contractually validated or invalidated, that is not the end of the story. There is still a need for a mechanism by which to assess whether the agreement was sufficient for it to be proper to hold the parties to it and to draw the jurisdictional consequences which would follow from it if it is. In the context of the Brussels I Regulation this was primarily done by requiring the agreement to jurisdiction to be in writing or evidenced in writing, or in a form which the parties have previously used and accepted, or in a form which is usual and used in the particular international trade in which the parties are engaged (art 25(1) Brussels I Regulation (recast)). The European Court has insisted, time and again, that the purpose of these ‘formal’ requirements is to guarantee that there was a genuine consensus, or, at least, to provide enough of a guarantee to justify giving jurisdictional effect to the supposed agreement (for example, Case C-106/95 Mainschiffahrts-Genossenschaft eG (MSG) v Les Gravières Rhénanes SARL  ECR I-911, para 15). It is debatable whether a writing requirement is capable of meeting the heavy and diverse burdens placed on it, for there is writing which is not the product of genuine agreement, and genuine agreements which are not reduced into writing. A broad and flexible principle of good faith should be able, but is also indispensable, to smooth the edges of the law and to yield a sensible answer.
The effect which an agreement on jurisdiction has may depend on whether it was, on a true construction, intended to be exclusive or non-exclusive: that is, binding the parties to litigate in or merely permitting one of them to bring the other before the designated court. The Brussels I Regulation provides that an agreement will be exclusive unless the parties have provided otherwise (art 25(1) Brussels I Regulation (recast)). This, though, is no more than a reflection of the rational rule that the nature and quality, content and extent of the agreement is a matter for the parties who should be permitted to fashion the agreement which they want, even if the impact that this agreement has on the jurisdiction of the court is then a matter for the jurisdictional law of the court in question. If there is dispute as to the meaning of words to define the agreement, a common lawyer’s instinct would be to refer the issue of construction to the law which governed the contract of which the agreement on jurisdiction is a term. This is justifiable in cases in which the agreement on jurisdiction was made as a term of a larger contract, but works less well where it was simply a unilateral statement of willingness to accept the jurisdiction of a court. In those cases it seems probable, though not entirely satisfactory, that a court will make recourse to its own domestic law. This may result in the agreement being construed contra proferentem, or its being made subject to a presumption in favour of one or another possible construction, but it will also tend to mean that the precise factual basis upon which the ultimate jurisdictional decision is taken may vary from court to court. It appears to be the law in some systems that a jurisdiction agreement which is expressed to be exclusive of all other jurisdictions if A sues B, but not exclusive of the jurisdiction of otherwise-competent courts if B sues A, is intrinsically invalid (Cass civ (1) 26 Sept 2012, nº 11–26.022,  J.Dr.Int’l 175,  ILPr 181). It is hard to see why this should be, for if the relationship between the parties is not a consumer contract, or anything like that, it is strange that the freedom of commercial parties to make an agreement on jurisdiction in the precise form which they agree to it should be constrained in this way.
Whether the particular dispute falls within the material scope of the agreement must also be a question answered, in the first instance at least, by rules of construction, for it is a matter of ascertaining the content and extent of the parties’ agreement. As with the previous point about exclusive or non-exclusive jurisdiction agreements, the point of first recourse will be to look to the law which governs any contract of which this jurisdictional provision is a term, for if the question is what the parties actually agreed to, the law which governs the agreement in which they set out their intentions is a good place to begin. Otherwise a court may be tempted to apply its own law to the question, which would be open to the same objections as set out above. The prevailing common law approach to such questions of construction is to give the words which define the scope of the agreement as broad an interpretation as they are reasonably capable of bearing. This is justified on the basis that it is hardly sensible for rational parties to include some kinds of dispute which might have been seen to arise between them, but not others, within the scope of an agreement on jurisdiction. Other systems might be more challenged by, or reject, a contention that general words of scope may embrace claims based on the alleged fraud or other serious wrongdoing of the party responsible for the wording of the agreement, and it is hard to deny that there is sense in such a view.
2. Issues ancillary to the existence and exercise of jurisdiction
It is in some respects clear, and in other respects debatable, that a jurisdiction agreement may do something other than play a part in a court’s determination whether it has or will exercise jurisdiction. In many legal systems, recognition of a foreign judgment (→Recognition and enforcement of judgments (civil law), →Recognition and enforcement of judgments (common law)) may be refused if it is shown that the foreign court took or exercised jurisdiction contrary to the terms of an agreement on jurisdiction. In the context of the Brussels I Regulation this is not the case (cf arts 34 and 35 Brussels I Regulation; art 45 Brussels I Regulation) – a state of affairs which is tolerable only because the court which exercised jurisdiction is to be assumed to have applied the jurisdictional rules of the Brussels I Regulation properly, with the consequence that the exercise of jurisdiction contrary to a jurisdiction agreement for the courts of a Member State should not occur. But if a court in a Member State exercised jurisdiction contrary to the terms of a jurisdiction agreement for a non-Member State, it appears that this furnishes no basis for the non-recognition of the judgment, which is a more challenging outcome. It might have been hoped that the Hague Choice of Court Convention would have dealt with this issue and reinforced a choice-of-court agreement by providing for the non-recognition of a judgment which conflicted with such an agreement, but the Convention failed to rise to the challenge.
A separate and distinct question concerns whether an agreement on jurisdiction imposes private and enforceable obligations on the parties to it, which may be enforced or reinforced by an →injunction ordered to restrain the party who proposes to bring proceedings in disregard of the agreement, or by a claim for damages for loss resulting from breach of the agreement. The view now widely accepted in the common law tradition is that where a jurisdiction agreement is a term of the contract, it is conceptually straightforward to conclude that it has been breached, and that the consequences of breach may be worked through in the ordinary private law of commercial →remedies. Even though the jurisdiction agreement serves a specific function as a matter of public law in relation to the jurisdiction of courts, there is no reason why it cannot also serve as the foundation for promissory, behavioural, obligations which each party undertakes to the other. To illustrate the point, suppose an agreement between A and B that proceedings will be brought only before the courts of state Y. This may not, under the jurisdictional law of state Z, prevent the courts of state Z from exercising jurisdiction. But it is still open to A to promise B not to bring proceedings against B before the courts of state Z. If A makes such a promise and then resiles from it, and that promise was contained in a contract, the conclusion that this amounts to a breach of contract by A seems naturally to follow. That being so, it is easy to see why a judgment from the courts of state Z, given against B, should not be recognized as res judicata. But it also explains why a court whose domestic law allows it to grant injunctions to restrain breaches of contract may see such an order as the proper response to a breach of contract. It may also support the argument that if B is able to prove the financial loss which he sustained by reason of his having been sued in state Z, when A had promised not to do this, he may maintain a claim for damages for breach of contract. Indeed, it is sometimes hard to appreciate why these ideas might be seen as being at all controversial.
That all being said, it may still be surprising that a common law court may order an →injunction, against someone in the position of A in the example described, which has the effect (whether direct, indirect or as a measure having equivalent effect) of interfering with proceedings lawfully – so far as the jurisdictional law of state Z is concerned – before the courts of state Z. A common lawyer may say, entirely correctly as a matter of common law, that the injunction has nothing whatever to do with the judge in state Z who, it will be assumed, has applied his jurisdictional law entirely scrupulously. The injunction responds to wrongdoing by a wrongdoer, and so strikes at an altogether different target, that is, A, who is doing the very thing he contracted with B that he would not do. A civilian lawyer may in turn regard that as sophistry and object that, in effect, the English court is interfering in matters which are exclusively for the presiding judge in state Z to deal with. Neither point of view can be lightly dismissed. Within the closed world of the Brussels I Regulation, the supervening principle is that the courts of one Member State have no power to interfere with proceedings before the courts of another, and that an injunction would have this impermissible effect. All theory aside, this is a perfectly sensible understanding of the economy of the Brussels I Regulation. But it can have no relevance in cases falling outside the scope of the Brussels I Regulation, and for which the only available answer is that each court will have to find the answer in the sensitive application of the rules of its own legal tradition.
As to whether breach of a jurisdictional agreement in a contract result in damages, it is hard to see why it would not, even though proof of the causing of loss might be challenging. However, if one rejects in limine the proposition that a jurisdiction agreement gives rise to any form of private law rights and obligations, this conclusion will presumably not follow. In England, there appears to be no judicial doubt about the sustainability of a claim for damages for breach of the personal obligations assumed by parties to an agreement on jurisdiction (see Starlight Shipping Co v Allianz Marine & Aviation Versicherungs AG (The Alexandros T)  EWCA Civ 1010, though the decision is actually the implementation of clear guidance from the Supreme Court).