Gavin,
Whilst all the above posts give good solid advice and it would be wise to heed what has already been posted, however when we applied I gave them nothing concrete at all just an assurance that we would abide by the rules and marry within the specified timescale and that worked for us and we got the visa. There must therefore be an element of luck involved and of course all the other information u provide will weigh in your favour if the ECO feels the relationship is genuine, so submit as much written evidence as u can and i am sure you be rewarded with a successful outcome.