Bit of a cheat really, in that it's not a joke, but I stuumbled across it this week and it made me laugh...a letter, sent by an MP to his constituents in 1734 after they wrote asking him to oppose proposals in the recent budget...
Gentlemen,
I have received your letter about the excise and I am surprised at your insolence in writing to me at all.
You know, as I know that I bought this constituency. You know, and I know, that I am now determined to sell it, and you know, what you think I don't know, that you are looking out for another buyer, and I know what you certainly don't know, that I have found another constituency to buy.
About what you said about the excise: may God's curse light upon you all, and may it make your homes as open and as free to the excise officers as your wives and daughters have always been to me while I have represented your rascally constituency.
Yours sincerely,
Anthony Henry MP