Sir Keir Starmer is braced for a revolt from his own party after allowing Natalie Elphicke, previously a right-wing Tory MP to join Labour.
Elphicke announced her defection from the Conservative Party yesterday just minutes before PMQs, with Starmer welcoming her to the party.
But former Labour leader Lord Kinnock warned Starmer against accepting everyone into the party.
He told the BBC: "I think we have got to be choosy to a degree about who we allow to join our party because it's a very broad church but churches have walls and there are limits."
Elphicke announced her defection from the Conservative Party yesterday just minutes before PMQs, with Starmer welcoming her to the party
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He said Elphicke had to decide whether she is "committed to the programme and principles of the Labour Party".
The MP for Dover, who was elected in 2019, took over from her husband who was jailed for two years in September 2020 for sexually assaulting two women.
After his conviction, Elphicke claimed the allegations were "false", saying he had been punished for being "charming, wealthy, charismatic and successful".
She was on the right of the Tory party, supporting Liz truss in the 2022 leadership contest and being a member of the pro-Brexit European Research Group.
Reacting to her defection, Labour MP Sarah Champion expressed concern over "some of the things Mrs Elphicke had said defending her ex-husband from the sexual abuse allegations", which she said "don't sit well with me at all".
A spokesperson for the Labour leader said: "All those issues have been dealt with previously both in Parliament and in public".
Elphicke was on the right of the Tory party, having supported Liz truss in the 2022 Tory leadership contest and being a member of the pro-Brexit European Research Group.
PA
Meanwhile, left-wing campaign group Momentum said: "This hard-right Tory should have no place in a Labour Party worthy of the name.
"It speaks volumes about Keir Starmer that he is welcoming her with open arms, while leaving Diane Abbott out in the cold."
Jenny Symmons, the GMB trade union boss, accused the Labour Party of having "welcomed her in" without "seemingly having standards you have to meet".
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Announcing her defection yesterday, Elphicke accused Sunak of failing to "keep our borders safe and secure", as well as "failing to build the homes we need".
The defection means that the Government's majority has more than halved since the general election, dropping from 80 to 38 seats.
Responding to Elphicke's defection, a Conservative Party spokesperson said: "The people of Dover and Deal will be disappointed having felt the impact of illegal immigration.
"They did have an MP who sat with the party fighting to tackle this issue head on, now they have had an MP in a party that has worked to block our plans to tackle illegal immigration 139 times.
"We wish Natalie well as she now has to support Labour's amnesty for illegal immigrants and one that directly opposes her own views - it was only last year that she penned an article titled 'Don't trust Labour on immigration they really want open borders'."