Labour has seen off a challenge from Nigel Farage's Brexit Party in a knife-edge by-election in Peterborough.
Mr Farage's newly-formed outfit lost out to Labour by 683 votes, in a blow to the former Ukip leader's hopes of building its recent European election showing.
As Theresa May formally bowed out as Tory leader, the Conservatives slumped to third place in what is traditionally a Tory-Labour marginal seat.
Meanwhile, Tory leadership hopeful Boris Johnson won a legal challenge, which means he will not appear in court over allegations he committed misconduct in a public office by “misleading the public” about Brexit.
And Jo Swinson and Ed Davey will go to head in the battle to become Lib Dem leader after being announced as the only two candidates running in the contest to replace Sir Vince Cable.
See below for live updates
Nigel Farage’s Brexit Party has failed to secure its first parliamentary seat as Labour snatched victory in the Peterborough by-election.
Unite activist Lisa Forbes was elected with a majority of 683 in the marginal seat vacated by disgraced MP Fiona Onasanya, who was sacked by her constituents for lying over a speeding offence.
Read our wrap of this fascinating by-election:
Labour is thought to have snatched victory from the Brexit Party due to its organisation on the ground.
Peterborough is traditionally a Tory/Labour marginal, and Labour won it in 2017 from Tory Brexiteer Stewart Jackson.
Momentum, the grassroots activist network, flooded the constituency with nearly a thousands activists in the weeks leading up to the vote.
Laura Parker, Momentum’s national coordinator, said: "This fantastic victory in difficult circumstances is down to the work of ordinary activists.
"Over the campaign, thousands of Momentum members knocked on doors and talked to voters in Peterborough, with more than 500 turning out for polling day and activists carpooling from across the country.
"Face to face conversations coupled with a radical, positive message about how we will transform Britain does win hearts and minds.”
Brexit Party leader Nigel Farage has tried to claim he never said his party would win in Peterborough.
"I always said we'd run it close, I never said we'd win it," he told BBC Radio 4's Today programme.
He said: "We came a very, very close second.
"But here's the important thing: eight weeks ago today the Brexit Party launched.
"What you have seen from this result last night is that British politics has fundamentally changed, it is no longer just two parties contesting."
He urged Tory supporters to vote tactically for his party to take on Labour in similar seats.
"The danger is that in seats like this the Conservatives split the Leave vote," he said.
Our sketchwriter Tom Peck has taken a sideways look at the Peterborough by-election.
He writes: "A fairytale night for Labour in Peterborough. A villain, a heroine and only the briefest flash of antisemitic controversy."
Humphrys denies this. McDonald says Trump did say it. Cue shouting.
Labour Against Antisemitism has put out a statement, describing Lisa Forbes' election as a "dark day" for Labour and calling for her to be suspended.
Spokesman Euan Phillips said: “When evidence of Ms Forbes allegedly antisemitic views emerged last weekend she should have been forced to stand down immediately, as urged by the Jewish Leadership Council and the Board of Deputies of British Jews.
"The Labour Party’s only Jewish affiliate, the Jewish Labour Movement also announced it would not be campaigning for Ms Forbes.
"Instead we witnessed the unedifying spectacle of dozens of Labour MPs - many of whom moderates, who had signed a letter of solidarity with the Jewish Labour Movement as recently as March - streaming up to Peterborough over the last few days to support a candidate who should have been taken off the ballot paper on Sunday.
"It appears that tribalism has trumped principle, and that the policy of zero tolerance for antisemitism has once again been abandoned by the Labour Party.
"We call for Ms Forbes to be suspended, and will be submitting a complaint to the party in the next few days.”
Theresa May will stand down today as Tory leader, amid recriminations over the party's performance in the Peterborough by-election.
As promised in her tearful statement on the steps of Downing Street on May 24, Ms May will formally quit as Tory leader ahead of the handover of power to a new PM at the end of next month.
"We are ready for a general election whenever it comes and we will will stop the Tories taking this country into a no-deal Brexit with all the threats to jobs that go with that."
Tory leadership hopeful Esther McVey has said the result in Peterborough is "the shape of things to come if we don’t deliver a clean Brexit on 31 October".
She said:“Our persistent thwarting of the referendum result shows that a Brexit Party vote will let Jeremy Corbyn into No 10 by the back door.
"Brexit is an opportunity to be seized not a problem to be mitigated. The UK can thrive after a clean break with the EU, and we will at last be able to show, once again, how a Conservative agenda can kickstart the economy.”
