Ms Flint was one of 19 Labour MPs to sign a letter asking the EU to secure a deal with the UK, and she was expected to vote for Mr Johnson’s deal in the Commons yesterday before that was delayed.
But Labour MPs including Rother Valley’s Kevin Barron, Great Grimsby’s Melanie Onn and Rotherham’s Sarah Champion, were threatened with deselection if they backed the PM by National Executive Committee (NEC) member and Momentum founder Jon Lansman,
Mr Lansman tweeted: “Johnson's deal will be a wrecking ball through the lives and well-being of ordinary people across Britain. Labour MPs cannot and must not vote for it. If they do, the NEC will have no choice but to replace them with a new, socialist Labour candidate at the next election.”
But Northern Labour MPs hit back.
Mr Barron said: “Threats such as this one will have no impact at all on the way that I vote.”
And writing in The Sunday Times today Ms Flint said: “As a democratic socialist with 40 years’ Labour Party membership, elected six times to serve as Don Valley’s MP, I received this threat in the same week that Don Valley MPs overwhelmingly reselected me.
“Well, I wasn’t elected to Parliament to bow to threats and intimidation. I won’t now.”
Explaining her choice to back Mr Johnson’s deal she said “my mining villages [...] voted for nationalism, the creation of the NHS and the minimum wage. For decades the European Union was not for them”.
She said: “More than 80 per cent of voters in my mining villages voted ‘leave’ in 2016.”
But she said as MPs voted for the Letwin amendment yesterday, which requires the PM to ask for a delay from the EU: “Yet again, those of us seeking a resolution to Brexit have been thwarted.”
She said: “As an MP who worked in good faith to improve the deal, I feel saddened.”
Speaking to Sky News’ Sophy Ridge this morning, Shadow Chancellor John McDonnell took a softer view than Mr Lansman.
Asked what will happen to Labour MPs who vote with Mr Johnson on Brexit, Mr McDonnell said: "The whips will deal with them in the normal way. Thank goodness I'm not the Chief Whip."
Asked about Labour MPs, such as Ms Onn and Ms Flint who would defy the whip Mr McDonnell added: "There has to be a respectful whip on a number of these things where we take into account people's views.
"People have to be listened to.”
He said "Melanie and Caroline have made detailed criticisms" of the deal that was put before Parliament.
He added: "That has to be listened to."