LONDON — Thursday, Halloween, Brexit Day, Britain Will Explode Day — or not.

Britain was supposed to take its most contentious political steps in decades by the strike of midnight and finally leave the European Union — three years after voting to leave it.

Weeks before the deadline, pro-Brexit politicians had warned that if the country did not leave the European Union on Oct. 31 as planned, there would be an explosion of riots and disorder in the streets.

“I think if we don’t leave on 31st of October, this country will explode,” Mark Francois, a hard-line Conservative member of Parliament, told BBC Politics Live in mid-September.

“Civil unrest could happen. I’m not saying it will — or that it’s even likely — but it is possible,” Conservative Party Chairman James Cleverly said at an event in late September.

But as the day began, with Britain no longer expected to leave the European Union until January after having receiving yet another controversial extension from Europe, the streets of London were hit by something else: an eerie sense of calm.

There was no carnage. No Brexit riots. No mass protests. Just thousands of tweets from people sharing sarcastic tales and snapshots from all the ways the country had (or had not) exploded.

While some people had run out of tea bags, others tweeted images of their cats fast asleep in tranquil homes. On one road a lone traffic cone had fallen on its side; on another, a handful of leaves had fallen from the branches of a rather naked-looking tree.

“Absolute bedlam,” tweeted one user as thousands joined the #BritainHasExploded movement to share their own horror stories.

Others looked for riots where there were none.

Both sides of the Brexit debate in Britain have been accused of scaremongering. Anti-E.U. voices had long criticized something they dubbed “Project Fear,” a catchall term for warnings about the potential negative economic and political repercussions of leaving the bloc.

But under Boris Johnson, prime minister since July and a major voice in the pro-Brexit camp, the British government had warned repeatedly about the risk of civil unrest in Britain if it did not leave by the Oct. 31 deadline.

Critics accused the government of a concerted effort to raise fears about a Brexit delay after an anonymous cabinet minister had told the Times of London that riots could occur if the 2016 referendum result is not honored.

“The message coming from Downing Street is we have to leave by October 31 or there will be riots,” former Conservative minister Dominic Grieve said this month.

Britain had originally been scheduled to leave the European Union on March 29, but the complicated task of negotiating its exit has led to that deadline being repeatedly delayed. Johnson had pledged no further delays, threatening a “no deal” Brexit that economists said could ravage the British economy, but was forced to ask for an extension after failing to pass his withdrawal agreement through Parliament in time.

Last month, Johnson said he would rather be “dead in a ditch” than ask for another delay in the Brexit process. Yet in October he was forced to ask Europe to push the deadline until the end of January.