Britain's opposition Labour Party began its bid to bring down Prime Minister Boris Johnson with a vote of no confidence, urging lawmakers to unite behind a caretaker government led by Jeremy Corbyn to prevent a no-deal Brexit.

Johnson has promised to take Britain out of the European Union by October 31, with or without a deal, setting the scene for a showdown in parliament where lawmakers are opposed to a divorce without a transition agreement.

In a letter to opposition party leaders and several senior Conservatives opposed to a disorderly exit, Corbyn said his "strictly time-limited temporary government" would delay Brexit and hold a general election.

He said Labour would campaign in the election to hold a second referendum on the Brexit terms, including an option as to whether the country should remain in the bloc three years after it voted to leave.

"This government has no mandate for No Deal, and the 2016 EU referendum provided no mandate for No Deal," Corbyn said. "I therefore intend to table a vote of no confidence at the earliest opportunity when we can be confident of success."

A spokesperson for Johnson's Downing Street office said the choice was clear: "This government believes the people are the masters and votes should be respected, Jeremy Corbyn believes that the people are the servants and politicians can cancel public votes they don't like."

Lawmakers return from their summer break on September 3, reconvening for a battle over Brexit that will determine the fortunes of the world's fifth-largest economy.

Johnson, who led the 2016 campaign to leave the EU, has staked his premiership on getting Britain out by October 31, prompting politicians from all sides to try to stop him.

On Wednesday he said those trying to block Brexit were engaged in "a terrible kind of collaboration," with Brussels after former finance minister Philip Hammond said parliament would block a no-deal exit, and the government must respect it.

Were Johnson's government to lose a no-confidence vote, lawmakers would have a 14-day period to try to form a new administration; otherwise a general election would be called, which could be held after the October 31 exit date.