The last line of defence for the legacy parties – the maxim that they are eternally protected from challengers by the first-past-the-post electoral system – has crumbled. At Peterborough last night the two-months-old Brexit Party came within 683 votes of winning its first Westminster seat.

Of course, there would have been considerable psychological advantage if the headlines had screamed “New party wins” and Nigel Farage’s infant political creation had added Peterborough to its European election laurels – such a narrow electoral miss is always tantalising. But the underlying realities that professional politicians and psephologists will discern from this result is, in terms of substance, every bit as seismic, if less spectacular, as a Brexit Party victory.

A party that did not exist two months ago, after sustaining the massive effort of winning a landslide in the EU elections, came late to Peterborough where Labour had been planning for a by-election from the moment its MP Fiona Onasanya was charged with a criminal offence, bolstered by polling data accumulated over decades and supported on the ground by local councillors.