SIR Keir Starmer is already facing mutiny after a Labour councillor backed Jeremy Corbyn.
Phil Graham endorsed the ex-Labour leader on his Facebook page on Friday saying there is “only one candidate” voters should consider.
Labour has since suspended Mr Graham as it is against party rules to support candidates opposing the party.
Mr Corbyn, who was blocked from standing for Labour, announced he will run as an independent in the Islington North seat he has represented for 40 years.
And insiders fear the race could turn nasty if hard left activists descend on the inner London seat.
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One told the Sun on Sunday: “The seat could be flooded with lefties on the day.”
Another added: “It’s going to be a toxic nightmare – both online and in person. Labour has a duty of care to the candidate and must work with police to ensure they have protection.
“It will be like no other election. There is going to be a big fallout whatever happens.”
In a video posted on X, Jeremy Corbyn said members of Islington North Labour were "denied the right to choose their own candidate".
He said: "I believe in democracy.
"I want our political parties to be democratic, but members of Islington North Labour have been denied the right to choose their own candidate, and alongside that the community as a whole has been disempowered because of that.
"So we have to stand up. We have to stand up and say, we're not taking this anymore, we will assert our rights.
"That's why I'm standing to be an independent candidate for the people of Islington North."
Polling guru Lord Hayward said Mr Corbyn could hold onto the seat.
He said: “Under ordinary circumstances an independent doesn’t stand a chance. But because of who he is and the reputation he has as a constituency MP I think he has a good chance of doing very well and possibly winning.
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Cllr Graham was contacted for comment.
