I completely disagree with you Day6 MPs stand for Parliament as individuals, it is only relatively recently that party affiliations have been put on ballot papers.
Local party members choose their candidate (or should do) after interviewing several and choose the one whose views are closest to theirs. The electorate, the vast majority of whom belong to no party at all, choose the candidate whose views best match their own.
As far as I can see these leavers have not substantially changed their political opinions, just the party they choose to support them in, so they are still the person the electorate supported at the polls.
Constituencies elect representatives not parties and anyone who votes blindly for one party and always that party, and probably would vote for a donkey providing it was wearing the right colour rosette, should be ashamed of themselves. To do that is to show a contempt for the opportunities democracy gives us.
At one point we had a local MP who changed alliegance part way through Parliament. He didn't change his views and if he had not retired at the next election, I would probably have voted for him, because whatever party he was in, his political views where in line with most of mine and I vote for the person best able to represent my views, I do not vote for a coloured rosette.