Tens of thousands of people opposed to Britain's withdrawal from the European Union gathered to march through central London on Saturday to demand a new referendum as the deepening Brexit crisis risked sinking Prime Minister Theresa May's premiership.

After three years of tortuous debate, it is still uncertain how, when or even if Brexit will happen as May tries to plot a way out of the gravest political crisis in at least a generation.

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May hinted on Friday that she might not bring her twice-defeated EU divorce deal back to parliament next week, leaving her Brexit strategy in meltdown. The Times and The Daily Telegraph reported that pressure was growing on May to resign.

May's sinking premiership

The Times quoted an unidentified Downing Street source saying that even her closest allies believed it was inevitable she would have to quit.

The Daily Telegraph said that senior ministers had urged May to go, and Buzzfeed reported that one lawmaker, a "whip" responsible for party discipline, had told her to set out plans to leave in the Sunday newspapers.

"She needs to set out a timetable for her departure and try to get her meaningful vote through. That's the best way forward," the Telegraph quoted an unnamed cabinet minister as saying.

"It's intolerable, the situation that we're in, and I'm afraid Theresa's the problem," Anna Soubry, a pro-EU lawmaker who left the Conservative party to join the Independent Group in February, told reporters.

"She has to go, and we need some temporary prime minister who can reach out, put the country first, and get this back to the British people. That's what we're all marching for today."

Betting odds indicate there is now a 20 percent chance that May will be out of her job by the end of this month, Ladbrokes said on Saturday.

March for a second referendum

While the country and its politicians are divided over Brexit, most agree it is the most important strategic decision the United Kingdom has faced since World War Two.

Pro-EU protesters gathered for a "Put it to the people march" at Marble Arch on the edge of Hyde Park around midday, before marching past the prime minister's office in Downing Street and finish outside parliament.

While there was no official estimate of the numbers, tens of thousands of people had allegedly gathered even before the event officially started. Organizers were confident that the size of the crowd would exceed a similar rally held in October when supporters said about 700,000 people turned up.

Two hundred coaches from around Britain were booked to take people to London for the march. One coach left the Scottish Highlands on Friday evening, and another left from Cornwall on England's western tip early on Saturday morning.

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A petition to cancel Brexit altogether gained 4 million signatures in just three days after May told the public "I am on your side" over Brexit and urged lawmakers to get behind her deal.

In the June 23, 2016 referendum, 17.4 million voters, or 52 percent, backed Brexit while 16.1 million, or 48 percent, backed staying in the bloc. But ever since, opponents of Brexit have been exploring ways to hold another referendum.

May has repeatedly ruled out holding another Brexit referendum, saying it would deepen divisions and undermine support for democracy. Brexit supporters say a second referendum would trigger a major constitutional crisis.

(Cover: People take part in the "Put It To The People March" in London, England, March 23, 2019. /VCG Photo)