Call the consulate would be my advice mate - they're really helpful at Hull and will tell you what's what IME. They always say you should have 6 months on your passport, I've no idea whether it's enforced.
Having said that, I'd get a new passport and then get your visa - then you won't have to worry about changing your visa to a new one while you are in Thailand. Also, replacement passports are much cheaper in the UK than in Thailand
Failing that get hold of KK - although he's missing in action it seems
You can apparently do a "same-day service" passport renewal in the UK - but I don't know anything about it