Actually, both MP's and constituents have it wrong.
The MP's serve the party leadership, and represent the will of the leadership, i.e., the oligarchy, to the people. That's why party headquarters dictates who is, and who is not, suitable to represent the party as a candidate for Parliament.
And the top-down control of House of Commons membership explains, in turn, why MP's are, for the most part, such a lame-brained lot. Who, after all, wants to spend their time dealing with complaints from annoying constituents with their endless problems and discontents, while, in Parliament, speaking and voting only as they are told by the party whips.
The result, obviously, is that the only people running for parliament are dim-witted megalomaniacs who think being an MP is somehow great, or less dimwitted megalomaniacs like Phony Blair intent on clawing their way to the top of the greasy poll for the purpose of personal enrichment and ego inflation.
