This is the phrase The Economist uses in a leader to describe the way in which the media construct the misfortunes of the government into a seemingly coherent narrative. After a while such a narrative becomes self-sustaining.
Of course, one very real defeat that the Government may face is in Crewe and Nantwich where the first local poll suggests a swing to the Conservatives of around 10 per cent, giving them a majority of 1,000. What may well happen is that there will be relatively little increase in the Conservative vote, but Labour voters may stay at home. Quite a lot also depends on whether any of the 16 per cent of voters plumping for the Liberal Democrats switch to the Conservatives.
Peter Riddell points out in The Times that by-elections are much rarer than they used to be. Since 2005, there have been an average of only just two a year, following a mere 1.5 annually over the previous four years. Between the mid 1960s and the mid 1980s the average was eight.
Gwynneth Dunwoody was rare in dying in harness. Now that they have good pensions, and face increased demands from their constituents, MPs usually stand down before the state retirement age.