[2006] EWCA Civ 1058, 7 July 2006. Appeal by GM against a decision ordering him to pay a sum to B in respect of work done at GM's premises. After B submitted an estimate in respect of refurbishment works, an oral agreement was reached between B and GM for the work to proceed. A list of the proposed works was attached to the estimate. Additional items of work were later done on GM's instructions. GM disputed the final bill on the grounds that many of the extra items formed part of the original agreement and had been paid within the contract price. The trial judge concluded that what the parties had agreed had been fixed at the time the agreement was made, and the subsequent conduct of the parties was not an aid to the original construction of the contract. He therefore refused to consider lists of work done that had been provided by B with interim invoices as a reliable guide to what the parties had believed to be additional items of work. He preferred B's evidence to that of M, and found that most of the items were true extras to the original agreement. "Held": where an agreement was partly written and partly oral, subsequent conduct can be examined to determine the parties' original intentions. In this case, the judge had been wrong to exclude evidence of the lists attached to the interim invoices. This error went to the heart of the case, as consideration of that evidence would inevitably have had some effect on the judge's views of B's credibility. Appeal allowed.