I sent 2 photos, letter and SAE to Sir David on: 30th July 2012, and today I recieved my photos back unsigned, plus a letter saying that Sir David only signs for charity.
address I used was:
Sir David Jason,
c/o Richard Stone Partnership,
Meg Poole,
Suite 3,
De Walden Court,
85, New Cavendish Street,
London
W1W 6XD