Changing policy
From what I've heard on Radio 4, writing e-mails has virtually no effect as e-mails are quick and easy to do. Writing (and posting) a snail mail letter is more effective as you have to put more effort into doing it in the first place. If I remember the discussion on last week's You and Yours correctly, I think the expert lobbyist was saying that if you send an e-mail you are assumed to be voicing your own opponion. If you write in politicians assume that at least 5,000 other people share your views.