LONDON — Tens of thousands of people marched on the British Parliament on Saturday, demanding another vote on Britain’s decision to leave the European Union. They wore T-shirts reading “This is what a European looks like” and waved signs urging “Bollocks to Brexit!”

The crowds were sizable and committed — organizers claimed 100,000 walked down Pall Mall — but the demonstrations were not seismic.

Although a couple of British politicians spoke at Parliament Square to the demonstrators, the leader of the opposition Labour party, Jeremy Corbyn, did not. (He was lightly booed when his name was mentioned.) The Labour leadership vaguely supports Brexit, as long as it is good for British workers.

So in keeping with all things about Brexit since the vote in June 2016 to leave the European bloc, the march seemed to do little to bring clarity to Britain’s messy exit from the European bloc.

Some demonstrators Saturday explained they were not necessarily against Brexit but wanted citizens to have another vote on any final deal that Prime Minister Theresa May negotiates in coming months.

“If it’s a no-deal or a bad deal, we should get a chance to look at it — because it is the decision of a lifetime,” said Peter Davies, 45, an office manager from London, while standing at Parliament Square.

Others wanted a redo referendum.

When asked whether British voters didn’t already settle the matter two years ago in their historic decision to leave the European Union, Davies answered, “I don’t know if people really knew what we were voting on.”

Others in the crowd said they supported Brexit, but a soft, gentle, friendly Brexit in which London would have more say over budgets or migration, but might stay in Europe’s customs union or single market — allegedly two red lines for May.

Victoria Lewis, 55, a math teacher from Brighton who wore a blue T-shirt that read “Citizen of Europe,” came out to rally “because I have three children and they need to be part of Europe. Humanity is about us cooperating, not putting up false barriers.” 

“It’s no accident there hasn’t been a war in Europe for 70 years.” she said. “It’s because we have been talking to each other and cooperating.”

There are growing fears that Britain will “crash out” of the European Union, with no agreement on future relations and trade — bringing about chaos.

This week, the executives of the aircraft manufacturer Airbus, which directly employs 14,000 people in the United Kingdom and supports another 100,000 in its supply chain, warned May about leaving the European bloc without a good deal.

“Put simply, a no-deal scenario directly threatens Airbus’s future in the U.K.,” said Tom Williams, the company’s chief operating officer, on BBC.

“We are seriously considering whether we should continue that development or we should find alternate solutions,” Williams said about plans to manufacture airplane wings in Britain.

BMW’s top executive, Ian Robertson, told reporters that U.K. car manufacturing was hurtling toward a cliff and that his company needs to know by the end of the summer what’s what — and not in October, as May plans. BMW employs about 8,000 people in Britain.

John Neill, chief executive of Unipart, a car-parts supplier that employs 6,000 people in Britain, told the Financial Times that carmakers would “find it very difficult to survive in the long term” if May chose a hard Brexit. 

May and her cabinet are divided over the best way forward on Brexit — and the prime minister has delayed, yet again, a clear declaration on what future relations with Europe should be. 

In an editorial in the Sun tabloid this weekend, British Foreign Secretary Boris Johnson warned May that those who voted for Brexit “don’t want some bog roll Brexit — soft, yielding and seemingly infinitely long” he said, deploying British slang for toilet paper.

Recent polling shows a stubborn split among respondents — although there appears to be a slight tilt against Brexit. In the last round of surveys by YouGov, 46 percent consider leaving the European Union to have been the wrong decision, while 43 percent think it was correct.

Campaigners against Brexit want another referendum, which they call a “people's vote,” to bail on leaving. Brexiteers say that the vote has already been held and that the “people’s will” should be respected. This is the prime minister’s position, too. 

Karla Adam contributed to this report.