Brecon was a reminder of dramatic days that made reputations and signalled the death of governments

There is such a thing as a brilliant by-election defeat. There is also such a thing as a crushing loss that destroys your party

It is too early to judge whether Thursday’s by-election in Brecon and Radnorshire will be remembered as a landmark on the road to stopping Brexit, or a mere footnote in the story of how the UK left the EU.

By-elections can appear momentous but then fade into obscurity. They allow protest votes when the public are not choosing a government, and can herald false dawns. Ukip won two by-elections in 2014 when Tory MPs Douglas Carswell and Mark Reckless defected to it, but only one seat at the following year’s general election.

The contests attract the media spotlight and can be painful for candidates. The nastiest I have covered was one of my first: the 1983 Bermondsey by-election in which the Liberals beat Peter Tatchell, the gay Labour candidate.