By Keir Mudie Imagine, one day, 20% of all the people you work with deciding to quit. Slightly unsettling, no? But another two Tory resignations this week and that’s the figure we’re at now. A fifth of them deciding enough is enough. Any general election sees its share of natural wastage. Some people just retire, for example. Others see it as a chance to get out of Parliament and make some proper money. But 20% is something, isn’t it? I spoke to one of those who has decided to stay and he told me the mood around the back benches is something else at the moment. He said: “I know people say, ‘I’…