Ms Onasanya, who was disowned by Labour after being jailed for lying over speeding ticket, lost her seat on Wednesday evening after thousands of constituents backed a move to unseat the independent MP.
A spokeswoman for Peterborough City Council said that 19,261 people signed the recall petition – triggered after her prison sentence – amounting to 27.64 per cent of those eligible to sign.
“This means that the petition is successful and the Peterborough parliamentary seat is now vacant,” said the council in a statement.
Seizing on the announcement, Mr Farage, the former Ukip leader, said the Brexit Party will field a candidate in the by-election – the first time the newly formed group will compete for a parliamentary seat.
Ms Onasanya’s former party welcomed the announcement that she had lost the Peterborough seat, and chair Ian Lavery said Labour “will vigorously fight the by-election here in Peterborough”.
Conservative parliamentary candidate for Peterborough Paul Bristow said: “The people of Peterborough deserve a better MP who will vote in parliament to deliver Brexit.
“I’m delighted this result gives local people the chance to make their voices heard and vote for a better MP – and it will be a choice between Jeremy Corbyn’s Labour candidate and me.
“We have had a Labour MP who hasn’t improved the prospects of the local community and has consistently voted against delivering the referendum result to leave the EU.”
Ms Onasanya was first elected to parliament as a Labour MP by a wafer-thin majority of 607 at the 2017 snap election – taking the seat from the Conservatives.
A year later, she was charged with perverting the course of justice after lying about a speeding offence. She was expelled by Labour after her conviction and served less than four weeks of a three-month prison sentence earlier this year.
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