You made the ultimate taboo - criticism of Labour party policy (and a Labour politician). That's heresy mate and you should be burned at the stake for being so "off message".
I don't think your letter was rude, you are perfectly entitled to your view and express that view to the person that represents you. I don't care whether you were rude, offensive, nasty or whatever, a person in his position should be polite and courteous regardless. His arrogance is breath taking. I thought Gordon Brown and his party were supposed to be listening, this plainly shows they aren't. Doesn't surprise me that he was a whip. His debating skills are pretty poor too, he doesn't argue any of your points and his letter is a basic STFU I was elected, put up with it. He's got a 10,000 majority and sits in a seat that will only ever vote Labour so he can tell you where to shove your vote.
Firstly I'd contact your local newspaper and let them print both letters. Let the local people decide who was rude or not. Secondly I'd email Guido Fawkes blog, I'm sure he'd be interested. The national press might catch on too.
"Reality is what it is, not what you want it to be." Frank Zappa. ----------- "The invisible and the non-existent look very much alike." Huang Po.----------- "A drowsy line of wasted time bathes my open mind", - Ride.