It was a big jolt on the road to Brexit, a sign that many of the 48 per cent who voted Remain still want Theresa May to pause and turn back. The Liberal Democrat victory in Richmond Park is most unlikely to stop Britain leaving the European Union, but it makes the small chance of delay slightly larger.

The election of a single MP pledged to vote against triggering Article 50, replacing the Eurosceptic Zac Goldsmith, does not change the arithmetic in the House of Commons much. There were perhaps 80 MPs, most of them Scottish Nationalists, prepared to vote against starting the formal procedure for leaving the EU. Now there will be 81, and with Sarah Olney the Lib Dems will be spared the embarrassment of an all-male contingent in the Commons.

But that still means there are about 550 who will vote for Article 50: the vast majority of MPs of both the Conservative and Labour parties.

What a sensational, media-saturated by-election does, though, is change the atmosphere, especially in the House of Lords. If the Supreme Court rules in January that Parliament must vote on Article 50, it will have to go through both Houses. Until this morning, the Lords would have felt bound by the referendum. Now there is evidence that the will of the people is not as clear-cut as the Prime Minister insists it is.

The House of Lords is still unlikely to delay Article 50. Angela Smith, the leader of the Labour peers, has said they will not obstruct it. But a few more Paleo-European peers in all parties and on the cross benches may be emboldened, and if anything else happens before the Bill is tabled they may be more emboldened still.

Theresa May must be regretting her mistake in failing to rush a Bill to trigger Article 50 through Parliament straight away. The longer the court case drags on, the more mood-shifting events such as by-elections can happen.

She may also be regretting her decision on Heathrow airport that caused this by-election, but I doubt it. She looks weakened now, but she would have looked weak too if she had tried to postpone the airports decision, yet again, until next year. Her working majority in the Commons will be cut from 16 to 14, assuming the Tories hold onto Stephen Phillips’s seat of Sleaford and North Hykeham in Lincolnshire in the by-election next week. (On Brexit, however, her majority is more like 470.)

The other significance of yesterday’s by-election is that it restores the Lib Dems to their rightful place as the protest party of British politics, shedding the memory of the coalition years. After their good showing in Witney, they have proved that in the right circumstances – one of the most highly educated, most Remainer seats in the country – they can take seats from the Government.

And, as Shirley Williams wrote here this week, by-election victories can change the political weather.

Full result of Richmond Park by-election

Sarah Olney, Lib Dem 20,510 49.7% +30.4 since 2015 election

Zac Goldsmith, Independent 18,638 45.2% -13.1

Christian Wolmar, Labour 1,515 3.7% -8.7 (lost deposit)

Others 620 1.4%

Turnout 53.6%