Anti-Brexit supporters have protested well into the night at key locations across London to condemn Prime Minister Boris Johnson's plan to suspend Parliament.

Key points: Critics have labelled Mr Johnson's move as a "coup"

Critics have labelled Mr Johnson's move as a "coup" More than a million people have signed a petition objecting to the suspension

More than a million people have signed a petition objecting to the suspension Protesters claimed the decision was undemocratic

Cries of "shame on you" and "stop the coup" could be heard from inside Britain's Parliament as a couple of hundred protesters gathered near the River Thames to wave EU flags and show their disgust.

The protesters claimed Mr Johnson's aim was to give his political opponents less time to block a no-deal Brexit before the October 31 withdrawal deadline.

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Mr Johnson insisted he was taking the step so he could outline his domestic agenda, and he shot down the notion that he was curbing debate, saying there would be "ample time" to discuss Brexit and other issues.

He had earlier said he asked Queen Elizabeth to give her speech that outlines the Government's legislative agenda on October 14, and that she had approved suspending Parliament between September 12 and October 14 — just ahead of the deadline.

"[Democracy's] taught from such a young age as such a vital thing about being a British person," said 17-year-old student Dylan Butlin.

"Today just completely ruins that, tramples it and throws it out."

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 1 minute 3 seconds 1 m 3 s Passions are running high among protesters on the streets of London.

"This is a coup. I know it because I've reported them … What we're seeing now is the theft of a parliamentary institution and tradition going back four hundred years," said left-wing journalist Paul Mason, who was addressing the protest.

British politicians, many of whom were on vacation, reacted with similar fury at the Prime Minister's move.

"Make no mistake, this is a very British coup," Labour Party MP John McDonnell said.

However, the criticism of Mr Johnson was not universal, with some politicians defending the suspension.

Anti-Brexit supporters gathered outside the Prime Minister's residence at 10 Downing Street. ( AP: Matt Dunham )

"This is a completely normal procedure," House of Commons leader and arch-Brexiteer Jacob Rees-Mogg told Sky News.

Asked what he would say to those who thought the move was undemocratic, the Conservative MP said they "didn't know what they were talking about — it's a normal functioning of our constitution".

More than a million people quickly signed an online petition objecting to the decision to suspend Parliament, and the pound fell sharply.

Protests outside the UK Parliament continued into the evening in London. ( AP: Vudi Xhymshiti )

The House of Commons will convene from September 3 to September 10 and then was scheduled to go on a break until October 9 — though politicians had suggested they might cancel that break and stay in session because of the Brexit crisis.

Twenty-five bishops from the Church of England released an open letter about their worries over the "economic shocks" of a no-deal Brexit on the poor and other vulnerable people.

Many politicians and ordinary citizens have been outraged by the decision. ( AP: Matt Dunham )

Politicians are already asking a Scottish court to rule that suspending Parliament is illegal.

If that fails, pro-EU legislators are also planning to try to pass a law banning a no-deal Brexit, although the Government has now sharply limited their time to do that.

Another option is to bring down the Government with a no-confidence vote. That would spark a 14-day period in which Mr Johnson could try to overturn the result.

European officials have also questioned Mr Johnson's decision to suspend Parliament. ( AP: Matt Dunham )

If he failed, there would be a general election — but the Government believes it would not have to be held until after the October 31 Brexit deadline.

Guy Verhofstadt, the European Parliament's chief Brexit official, called Mr Johnson's move "sinister".

"As a fellow parliamentarian, my solidarity [is] with those fighting for their voices to be heard," he tweeted.

"Suppressing debate on profound choices is unlikely to help deliver a stable future EU-UK relationship."

Demonstrators in London chanted "stop the coup". ( AP: Matt Dunham )

Reuters/AP