I had my mam write me a cheque as I don't have a chequebook!
It's worth while writing a little cover letter noting everything you've included. Do as much as you can to make their job easy and it'll pay off! I sent an SAE and asked for the title and all the docs I had sent to them to be returned to me which apparently they don't usually do - they stamped it with a DVLA stamp and sent it back so I have it to keep forever which is a nice touch in the history folder if I ever come to sell it!
As above it depends who's desk it lands on, but the easier you make it the quicker you'll have it back.
Mine was about 10 days from start to finish.