LONDON (Reuters) - Hundreds of thousands of Britons opposed to their country's withdrawal from the European Union (BRICCET) marched in central London on Friday to demand a new referendum on secession in an escalating crisis that threatens to keep Prime Minister Theresa May in power.

Protesters marched in central London, raising banners saying, "The best agreement is not to go out" and "We demand a vote for the people" at a rally organizers described as the biggest protest against secession to date.

Although there are no official estimates of the number of participants in the demonstration on Saturday, organizers said hundreds of thousands of demonstrators gathered before the march began.

After three years of intense debate over the BRICEST, there is still uncertainty as to how and when to leave the bloc, amid May's attempts to resolve the most difficult political crisis in the country in nearly 30 years.

May hinted yesterday that it may not re-propose an agreement reached to withdraw from the European Union to parliament to vote for the third time next week if there is not enough support for approval. The Times and the Daily Telegraph reported that pressure was mounting on May to resign.

Gareth Ray, 59, who came from Bristol to participate in the demonstration, told Reuters: "I would feel a different feeling if Brikast is a well organized process and the government has made adult decisions, but it is total chaos."

"The country will be divided regardless of what happens and it is bad to be divided into a lie," he said.

Organizers said more than a million people joined the protest to go beyond a similar crowd organized in October that supporters said about 700,000 people had joined.

The figure could not be independently verified, but a Reuters journalist said the march was so huge that some crowds were diverted away from the main track.

Police declined to provide estimates on the number of protesters.