Jeremy Corbyn has asked the UK's most senior civil servant to intervene to stop a no-deal Brexit from happening during a general-election campaign.

The Labour leader is concerned that the UK could leave the European Union without a deal on October 31, the scheduled exit date, while the country is in the middle of an election campaign.

He accused Prime Minister Boris Johnson of planning an "unprecedented, unconstitutional and anti-democratic abuse of power."

There has been speculation that MPs could force a no-confidence vote to bring down Johnson's government days before the Brexit deadline.

Johnson reportedly plans to refuse to resign if he loses a no-confidence vote and would instead call for an election in the days after a no-deal Brexit.

Labour Party leader Jeremy Corbyn has called on the United Kingdom's most senior civil servant to intervene to prevent Prime Minister Boris Johnson from forcing a no-deal Brexit in the middle of a general-election campaign.

Corbyn on Thursday wrote to Mark Sedwill, the cabinet secretary, accusing the prime minister of planning an "unprecedented, unconstitutional and anti-democratic abuse of power," after it was reported that Johnson could hold a general election the day after Brexit. The UK is set to leave the European Union on October 31.

Corbyn's letter came amid speculation that members of Parliament could stage a vote of no confidence in Johnson before October 31 to try to stop a no-deal Brexit — a vote that, if successful, would trigger a general election.

In his letter, the Labour leader asked for clarification around the rules of purdah, designed to prevent a government from making major policy decisions during a general-election campaign.

He asked Sedwill to clarify whether, if the UK was set to leave the EU during an election campaign, the government would legally be required to seek an extension to Article 50 to allow the next government to make a decision about Brexit once the campaign is over.

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"Forcing through No Deal against a decision of Parliament and denying the choice to the voters in a general election already underway would be an unprecedented, unconstitutional and anti-democratic abuse of power by a Prime Minister elected not by the public, but by a small number of unrepresentative Conservative Party Members," he wrote.

"I am therefore writing to seek your urgent clarification on the proper application of 'Purdah' rules in such a scenario and the constitutional implications of failing to abide by those rules."

Corbyn. Dan Kitwood/Getty Images

Corbyn's letter was released after Downing Street repeatedly refused to rule out delaying an election until the few days after Brexit on October 31, even if MPs trigger one beforehand by voting to oust Johnson in a bid to stop a no-deal exit.

Many MPs determined to stop a no-deal Brexit believe that a confidence vote that triggers a general election is the last mechanism available to prevent the UK from crashing out of the EU with no deal.

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Under such a plan, MPs would vote to topple Johnson's government, force the prime minister to resign, and use an allotted 14-day period to try to find a majority for an alternative government comprised of opposition MPs and a small number of Conservatives.

But Dominic Cummings, the most senior aide in Downing Street, has reportedly warned that Johnson would simply refuse to resign during the 14 days following a vote of no confidence, allow the UK to crash out of the EU, and then call for a general election.

Asked by the BBC on Thursday whether he would resign after losing a confidence vote, Johnson declined to answer.

"I think that what MPs should do and what I think they've already voted to do, when triggering Article 50 and reconfirmed several times, is honour the mandate of the people and leave the EU on October 31," he said.