This is sort of why I'm becoming less partisan.
I don't doubt there are MPs who are decent in every party. Equally both Labour and Tories will have people in safe seats who know they can just get by. And there's no doubt there are too many "professional politicians" out there. But the answer...
Presumably, when the swamp gets drained, the sorts of people who'll be first down the plughole will be those who avoid UK tax by being shareholders in shady offshore companies......
https://www.theguardian.com/world/2016/oct/15/panama-papers-reveal-offshore-secrets-arron-banks-brexit-backer