You can be formal or less formal:
The formal approach is to address it to: The Prime Minister, 10 Downing Street, London SW1 and start the letter "Dear Prime Minister".
The less formal approach is to address it to: The Rt Hon David Cameron PM, 10 Downing Street London SW1 and start the letter "Dear Mr Cameron"
Addressing him as "Dear Dave" probably won't get a reply.
snob@whitehall.com.au
David Cameron House of Commons LondonSW1A OAA That address is same to contact any Member of Parliament of whatever political party
No. David Cameron is not racist.
No, David Cameron is not dyslexic.
David Cameron's wife's name is Samantha Cameron.
Samantha Gwendoline Cameron is the name of David Cameron's wife.
No. David Cameron's parents were married in 1962, and David Cameron was born in 1966.
David William Donald Cameron
David Cameron's hair is brown
No. David Cameron is not racist.
David Cameron is the Prime Minister of The UK
David Cameron was born in London, United Kingdom