Note that what this case does not do, and LJ Coulson made it quite clear that this was not an issue he was considering, is to give a general statement on a contractor’s entitlement to an extension of time in circumstances of concurrent delay. The court was solely considering the bespoke concurrency clause agreed by the parties. LJ Coulson, agreeing with Mr Justice Fraser, said that: “In my view, clause 2.25.1.3(b) is unambiguous. It plainly seeks to allocate the risk of concurrent delay to the appellant.The consequence of the clear provision was that the parties have agreed that, where a delay is due to the contractor, even if there is an equally effective cause of that delay which is the responsibility of the employer, liability for the concurrent delay rests with the contractor, so that it will not be taken into account in the calculation of any extension of time.” In light of the Judge’s conclusion, the only remaining issue was whether there was any reason in law why effect should not be given to that clear provision. NMBL suggested, “boldly” in the words of LJ Coulson, that the prevention principle was a matter of legal policy which would operate to rescue NMBL from the clause to which it had freely agreed. This suggestion was rejected for the following reasons: (i) The prevention principle is not an overriding rule of public or legal policy, like for example the rule which strikes down liquidated damages as a penalty. (ii) The prevention principle is not engaged because pursuant to clause 2.25.5, “any impediment, prevention or default, whether by act or omission, by the Employer” gave rise to a prima facie entitlement to an extension of time. (iii) The prevention principle has no obvious connection with the separate issues that may arise from concurrent delay. (iv) Clause 2.25.1.3(b) was designed to do no more than reverse the result in the Walter Lilly case that where delay is caused by two or more effective causes, one of which entitles the contractor to an extension of time as being a relevant event, the contractor is entitled to a full extension of time. (v) Clause 2.25.1.3(b) was an agreed term. This was the most important of all.