Just two weeks are left until polling day in three crucial by-elections: Uxbridge and South Ruislip, Selby and Ainsty, and Somerton and Frome. Though bookies are hardly infallible, you can’t really argue with odds of 20 to 1 “on” of the Liberal Democrats’ Sarah Dyke being returned in Somerton on a swing of at least 40 per cent; it would …