Just how bad are things for Gordon Brown? As bad as for John Major after Black Wednesday? As bad as for Margaret Thatcher after the poll tax? As bad as for Jim Callaghan after the winter of discontent? As bad as for Edward Heath after the three-day week? As bad as for Harold Wilson after In Place of Strife?

All of these events are remembered by older British electors as the writing on the wall. The point of no return is a familiar landmark in political history, more clearly signposted in retrospect. And the unforgiving rule today – one strike and you are out – raises the stakes.