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Others argue that the exit strategy itself is not given a sufficiently high priority during contract negotiations - as some customers are now finding to their cost. Effective exit clauses help to prevent major problems since they tend to compel the supplier to perform to agreed levels.

Helpfully, Zrimsek has drawn up a list of what he terms 'best-in-class' clauses for IT contracts. Above all, he says, the customer should be given the right to terminate the contract if their supplier is acquired.

The agreement should also stipulate that the acquiring company must take on the original contract's obligations. In the event of an IT services merger, the contract should stipulate that billing rates are pegged at the original contract levels so that a change in ownership will not affect the cost of a project. In addition, there should be a clause granting the customer the right to review and approve a new consulting team.

That is not all. The IT director should ask that a fresh contract be drawn up with the new supplier, says Gartner's Zrimsek. This is when it may get trickier. The IT director, he adds, should at least make a case for including a so-called 'termination for convenience' clause, which enables the customer to terminate the contract for any reason, giving just 30 days notice.

The contract should also spell out the triggers for termination and the mechanism to be followed, such as notice periods for a breach of contract. But contracts are often unclear on such points and the act of proving a breach can be fraught with difficulty.

Without the proper records and checks and balances, it often turns into one person's word against another. "When you are terminating a contract, the stakes are very high," says Julian Stait, a partner with law firm DLA. "If you get it wrong, there could be a very high level of exposure."

See you in court

Historical precedent provides ample reasons for customers to be both encouraged and alarmed by the prospect of engaging in a contractual dispute.

In the past, a determination on both sides to protect corporate reputations has meant that such disputes have tended to be settled out of court. Occasionally, and memorably, warring parties have preferred to fight it out in public.

What some of the great IT legal disputes of the last decade reveal is that companies will sometimes go to considerable lengths to extract themselves from a contract. The Co-operative Group's long-running dispute with ICL (now Fujitsu) is a case in point. A row erupted in 2001 after the Co-op claimed that an electronic point of sale system being implemented by ICL was not up to an acceptable standard.

During the trial, ICL claimed that the Co-op, 12 months into the 15-month project, did not want the project to proceed and sought to undermine it. Evidence presented at the trial appeared to suggest that Co-op managers had a festering grievance about ICL because of concerns over an ICL project with Co-op's funeral business. One Co-op email read out in court said that ICL should be set up to extract a "pound of flesh".

But, as Stait says, "it is very difficult to prove a breach [of contract] and anyway, there are always two sides to the story."

So it has proved in the Co-op/ICL case. The Co-op's hearing ended with the Court of Appeal ordering a retrial for later in 2004 because the judge felt it was highly unlikely that Co-op managers would deliberately place a vital £12 million IT project at risk. Fujitsu says it will appeal to the House of Lords.

With a possible retrial pending, it is still too early to say what the wider significance of the Co-op case will be. But its impact is unlikely to be as important as a case from over a decade ago - the Salvage Association versus CAP Financial Services - which resulted in the reinforcement of customers' exit rights. The dispute proved to be an important test case over the use of contentious 'limitations clauses', which set a ceiling on how much a supplier has to pay in penalties if an IT project ends in failure.

The complexity of the action was reflected in the fact that the trial lasted for 72 days. But, in essence, the Salvage Association's case hinged on whether CAP (now part of Cap Gemini Ernst &Young) had acted fairly in putting a clause in the contract that limited its liability to only £25,000. For the salvage industry group, there was a lot at stake - losses on the project amounted to £800,000, making its liability £775,000. But the High Court ruled that the limitation clause was made invalid since it was unreasonable to expect a customer to carry losses caused largely, if not entirely, by a supplier.

Before the Salvage/CAP case, organisations occasionally felt locked into bad IT projects because they were worried about being left with big losses (and unfinished software) if they were to terminate a contract early. But perhaps the most important boost to customers wanting to be freed from failing projects came back in the early 1990s when St Albans District Council fell out with ICL over a two-year scheme to roll out a council tax calculation and administration system.

The case had important implications for customer-supplier relations. Ian Lloyd, a law professor at Strathclyde University, describes it in his 2000 book, Legal Aspects of the Information Society, as "undoubtedly the most significant precedent in the field of IT law".

The dispute concerned the point at which software under development became the finished article and, as a result, at what stage errors and bugs could be regarded as breaches of contract. ICL developed the tax system over the course of a two-year period, adding new functions as it went.

It was a fine idea in theory, but in practice ICL struggled to meet the agreed deadlines and the software did not always calculate tax bills correctly. St Albans sued ICL for £1.3 million in damages - the net loss to the council of the miscalculated bills.

ICL argued in court that the council understood that the software would be a 'work in progress' and that its performance should be judged only at the end of the implementation period. Defects that might have occurred during that period should therefore be discounted.

But the court was not persuaded by this view, ruling that ICL should be held responsible for failures that occurred at any stage of the product release, especially since the system was supposed to be carrying out important calculations early on.

The ruling gave customers a stronger case if they wished to withdraw from contracts early. But, although some of the above cases have shifted the balance of power towards the customer, that does not necessarily mean that terminating IT contracts has become an easier task.

Exiting from a contract can enable an organisation to cut its losses when a supplier is acquired - especially when that event threatens the product's future. But ensuring that it has that option in the first place, and making the process as painless as possible, takes considerable foresight.