British Prime Minister Boris Johnson sparked fury Wednesday among pro-Europeans and MPs opposed to a no-deal Brexit by forcing the suspension of parliament weeks before Britain's EU departure date.

The pound slid on the surprise news, which opponents branded a "coup" and a "declaration of war" but Johnson claimed was necessary to allow him to pursue a "bold and ambitious" new domestic agenda.

It came a day after opposition parties vowed to seek legislative changes to prevent a no-deal Brexit.

Queen Elizabeth II approved the request to end what has been the longest session of parliament in nearly 400 years in the second week of September, and reopen it on October 14 -- just over two weeks before Brexit.

Thousands of people protested in London, Manchester, Edinburgh and other cities, while an online petition decrying the decision had garnered more than one million signatures within the space of a few hours by late Wednesday.

At the biggest rally, crowds gathered near parliament in London chanting "stop the coup" and waving EU flags.

"Parliament will have the opportunity to debate the government's overall programme, and approach to Brexit," Johnson, who leads the Conservative party, vowed in a letter to MPs.

However, his decision incensed lawmakers vehemently against Britain leaving the EU without a deal on October 31 as they will now have less time to try and thwart such a scenario.

Jeremy Corbyn, leader of the main opposition Labour Party, denounced the move as "a smash-and-grab against democracy" and reiterated he would call a no-confidence vote in Johnson's government, which commands a majority of just one seat.

Former chancellor Philip Hammond also pledged to keep fighting against no deal.

"It would be a constitutional outrage if parliament were prevented from holding the government to account at a time of national crisis," he said.

- 'Compliant PM' -

US President Donald Trump weighed into the row by praising Johnson as "great" and claiming it would be "very hard" for Corbyn to topple him in a no-confidence vote.