Fiona Onasanya has been expelled by Labour with the party prepared to "actively support" a petition to remove her as an MP.
The MP for Peterborough was suspended by the party immediately after being found guilty a fortnight ago of perverting the course of justice following a retrial at the Old Bailey.
The party's chair Ian Lavery MP confirmed in an interview with the Peterborough Telegraph this evening that Ms Onasanya was expelled by Labour the following the day.
Mr Lavery said the people of Peterborough had been "failed" by Ms Onasanya and that he was "absolutely confident" Labour would win a by-election should one be held here.
Ms Onasanya was a rising star in the Labour Party and had aspirations to be the country's first female, black Prime Minister after winning the seat by 607 votes in June 2017.
However, the trained solicitor's reputation is in ruins after a jury unanimously found her guilty of lying about who was the driver of her Nissan Micra which was caught speeding in Thorney in July 2017.
Ms Onasanya has kept a low profile since the verdict and not spoken about it in public despite attempts by the PT to contact her. She was spotted outside her home in Peterborough earlier today as she awaits sentencing at a later date.
The MP used her column for the PT last week to strongly hint that she wants to carry on as an MP. She wrote about fighting “injustices”, adding: “There is still much more to be done, and you can rest assured that I will continue to do so as your representative in the corridors of power.”
But Mr Lavery declared that Ms Onasanya should immediately step down an as MP, echoing a statement given by the party following her conviction.
The party chair said: "Fiona isn't a member of the Labour Party, she isn't a Labour MP. People here in Peterborough voted for a Labour MP. She was suspended from the Labour Party and she was expected to resign. She hasn't resigned, regrettably.
"We would still at this very last moment suggest the best thing would be for Fiona to act responsibly and resign her position as a Member of Parliament.
"We would be raring to go for a by-election. We're up for it. The people in Peterborough want a Labour MP - they voted for a Labour MP the last time and I'm absolutely confident from what we have to offer we would win a by-election in the very near future if one was to be held."
Mr Lavery, the MP for Wansbeck in Northumberland, was speaking to the Peterborough Telegraph - which broke the story of Ms Onasanya's court trial - before attending an emergency meeting with the Peterborough Labour Party to discuss the constituency party's next actions.
He said should Ms Onasanya lose her seat following her sentencing the party will want a candidate in place as soon as possible.
The process for choosing a candidate, and whether there would be an all-woman shortlist, has yet to be decided, but Mr Lavery said the party wants "local people selecting their representatives".
It has been reported that Ms Onasanya was selected by a panel on the party's governing body the National Executive Committee.
If Ms Onasanya is sentenced to a year or more in prison (including if it is a suspended sentence) then she will lose her seat.
Any custodial or suspended sentence of less than a year which is not appealed would automatically trigger a recall petition.
If 10 per cent of her constituents signed it within six weeks, Ms Onasanya would lose her seat and a by-election would be triggered, which she could stand in.
Mr Lavery said should Ms Onasanya remain as an MP Labour would not "cosy up to her" in an attempt to secure her support during crucial votes in the House of Commons.
He also refuted any suggestions that voters might punish Labour at the next election in Peterborough for previously selecting Ms Onasanya as its candidate, stating that "ordinary people" realised the party had acted "responsibly" by suspending her immediately after the guilty verdict against her.
Asked if Labour would campaign for residents in Peterborough to sign a recall petition should one open up, Mr Lavery replied: "Labour would actively support the recall of an MP under the Recall of MPs Act 2015."
His message to Peterborough constituents was: "You voted for a Labour Party person. Unfortunately the people of Peterborough were failed. We want a Labour Party MP here who will do the people of Peterborough a great service."
The Peterborough Labour Party has not commented on the guilty verdict against Ms Onasanya ahead of its emergency meeting this evening.
Ms Onasanya is due to be sentenced later this month, but a date has not yet been fixed.
Ms Onasanya’s brother Festus is due to be sentenced on the same day as her after pleading guilty to three counts of perverting the course of justice, including in relation to his sister’s case.