I've selected a very local builder to build my extension. Initial quotes from various potential companies were very similar, so in the end it came down to which builder was more flexible and had the better references. I think that I've done sufficient due diligence now, so this evening I awarded the work, subject to contract.
It looks like we should be able to get the job under way in early June - just over a month from now. I'm allowing four months for completion, so everything should be done and dusted before the nights start drawing in too much.