Lazarus has risen. The Lib Dems' Richmond by-election triumph confirms their return as an insurgent force in British politics. Tim Farron's party overturned Zac Goldsmith's elephantine 23,015 majority with a vintage swing of 21.7 per cent (their biggest since 1997).

The victory will be commonly described as a "shock" today. But all the signs, as Stephen noted earlier this week, were there. The Lib Dems won a swing of 19 per cent in the recent Witney by-election and have long been advancing locally. In Richmond, they turned an ostensible referendum on Heathrow (the trigger for Goldsmith's resignation) into one on Brexit. The seat, which voted 69-31 for Remain, revolted against the incumbent's Leave stance. In a competitive field, Goldsmith (who lost with dishonour in London) may have had a worse 2016 than any other politician.

By not fielding a candidate, the Conservatives avoided the humiliation of defeat. But the result is also a rebuke - and a warning - to them. Were last night's swing replicated on a national level, the Tories' majority wold be wiped out. By-elections are a historically poor indicator of general election results but marginal MPs will still endure sleepless nights. If Goldsmith can squander a majority of 23,015, they will ask, what chance for us? Bath, Cheltenham, Kingston and Surbiton, and Twickenham are in the Lib Dems' sights (though its former south west heartland is staunchly eurosceptic).

Even before Theresa May became Prime Minister, new MPs pleaded with her not to go to the country for fear of a Lib Dem revival. Their warnings have been vindicated. An early general election, which May has long inclined against, is now even less likely.

Since May became PM, much of the political pressure on her has been for a "hard Brexit". But Richmond gives supporters of a "soft" exit (or none at all) a rallying point. For the first time, the principle of blocking Brexit has been endorsed at the ballot box. Marginal Tories risk being caught on the wrong side of their constituents.

Though the Conservatives have the most to fear from the result, it will also deepen Labour anxieties (it won just 3.7 per cent in Richmond). If Brexit becomes the new dividing line in British politics, the party risks a three-way squeeze between the Lib Dems, Ukip and the Tories. As Labour learned to its cost in Scotland, referendums can have painful afterlives.