Sally Gimson was picked for the seat by the constituency Labour Party (CLP) at the end of October but has now been told by Labour’s National Executive Committee (NEC) that she cannot stand because of allegations over her conduct at a local meeting in Holborn and St Pancras.
But Ms Gimson has called the saga a “kangaroo court” and Lord Mann, who stepped down last month, said they were “trumped up charges” and added: “The people of Bassetlaw will not accept an outside stooge imposed by the cult around Corbyn. This is the mother of all Momentum stitch ups.”
Shadow Brexit Secretary Keir Starmer was campaigning with Ms Gimson as recently as this weekend.
A statement from Holborn and St Pancras CLP, where Ms Gimson is currently based, said: “At no point was the CLP contacted by the NEC regarding these complaints and there has never been any prima facie evidence provided to the CLP that would warrant any formal investigation into Sally Gimson’s conduct at any of our meetings.”
They also said Ms Gimson, who had the support of her home CLP and the Bassetlaw group, submitted more than 20 pieces of evidence in her defence but these were not accepted.
But it is understood Labour denies the complaints were only about behaviour in a CLP meeting and that the complaints related to serious allegations concerning protected characteristics.
News website LabourList said one of the complaints claimed Ms Gimson shouted at a disabled Labour member, which she has denied.
But Ms Gimson said: "I have been condemned by a kangaroo court.
"I have been thrown out on trumped up charges that only came to light five days ago.
"From the outset I was not the preferred candidate, a Londoner and Keir Starmer's constituency and a firm remain.
"The NEC had already worked to keep the Bassetlaw applicant off the longlist and I got through the process with the belief that the favoured candidate would annihilate me.
"Their calculations were wrong and my strong campaign, speaking and meeting with local members meant that I won the selection.
"On Friday November 1, I received a letter from the NEC informing me that they had received a series of internal complaints from the CLP in Camden.
"On Monday I was subjected to an interview over the phone where they would not give me the detail of the complaints, who had made them, they would not consider my witness statement, would not tape the meeting and ended the meeting before we had gone through all the issues.
“I was threatened not to tell anyone about what was happening and the consequences of this have kept me silent so far.
"Transparency, openness and democracy has been thrown out the window."
A Labour spokesman said the party did not comment on internal selection processes.