An MP has been given a three-month jail sentence for lying to avoid a speeding ticket, and is expected to try to remain in office despite calls to stand down.

Fiona Onasanya, the MP for Peterborough and a former Labour whip, was sentenced on Tuesday for perverting the course of justice following a retrial.

Sources close to Onasanya, the first serving MP to be jailed in 28 years, said she was believed to be planning to return to work as an MP once she leaves prison. She will continue to be paid while in prison, parliamentary sources confirmed.

Labour and the Conservatives have called for her to “do the decent thing” and resign immediately.

Onasanya appeared at the Old Bailey in London on Tuesday to be sentenced alongside her brother Festus Onasanya, who pleaded guilty to three similar charges and was sentenced to 10 months.

Mr Justice Stuart-Smith said: “It’s a tragedy that you have found yourselves here and in this predicament but it’s a tragedy that you have brought on yourselves.”

Onasanya did not react to the verdict but was taken away to begin her sentence.

Under laws introduced in 2015, any prison term, even a suspended sentence, leads to a recall petition, which will be open for six weeks and can force a byelection if signed by 10% of voters in a constituency.

Because Onasanya, 35, has appealed against her conviction, this may not happen for several months. The recall petition cannot be opened until any appeal process has concluded.

Staff in her constituency office said they would continue to work through her sentence. “Nobody who has issues on immigration, housing local services etc should be punished for what happened,” Matt Turner, her press officer, wrote on Twitter.

A former councillor, Onasanya was selected by Labour in 2017, shortly before the general election. Her victory over the Tory incumbent Stewart Jackson by 607 votes was unexpected. When she was interviewed shortly afterwards, Onasanya said she would like to become Britain’s first black female prime minister.

The jury was told the MP’s Nissan Micra was caught speeding at 41mph in a 30 mph zone in July last year. The prosecution alleged she went on to collude with her brother Festus to avoid a speeding ticket in a series of exchanges with the police.

The court was told she was sent a notice of intended prosecution to fill out, but it was sent back naming the driver as Aleks Antipow, an acquaintance of her brother who was away visiting his parents in Russia.

In remarks at sentencing, the judge said her decision to remain as an MP was beyond the powers of the court.

“As things stand, it is not right to say that you have lost everything. You have decided to remain as a member of parliament despite your expulsion. It is well beyond the remit of this court to speculate on what the future holds for you as member of parliament for Peterborough.”

Referring to the fact she has multiple sclerosis, Stuart-Smith said her health and her previous good character had been taken in to accounts during sentencing.

“I also take into account your illness though there is no medical evidence to suggest that your unfortunate condition would make a significant difference to your ability to sustain a period of imprisonment,” he said.

He said he had to give her a custodial sentence on the basis that she had took a series of “disastrous” decisions from November 2017 until her trial that were designed to pervert the course of justice.

“There cannot be one law for those in positions of power, privilege and responsibility and another for those who are not,” he said.

Christine Agnew QC, counsel for Onasanya, said the case had had a disastrous impact upon her client’s life. “She continues to stand as an independent MP and her only reason for that is because it is her only source of income,” she said.

Major political parties have been campaigning in Peterborough in expectation of a byelection since Onasanya was found guilty in December.

A spokesman for the Labour party said the sentence gave the MP an opportunity to act honourably and resign from parliament. “If Fiona does not resign, Labour will support local residents in their efforts to trigger a byelection through a recall petition,” he said.

The Conservatives also called for Onasanya to resign. “She cannot possibly represent her constituents from prison and should do the decent thing and immediately step down,” a spokesman said.

Onasanya is the first sitting MP to be jailed since Terry Fields was sentenced to 60 days for failing to pay his poll tax bill in 1991.

Festus Onasanya, 34, from Cambridge, pleaded guilty to three counts of perverting the course of justice over speeding, including for the 24 July incident.