The People's Vote campaign for a second referendum on Brexit has announced a march the weekend before the UK leaves the EU.
The "put it to the people" march will call for the public to be given a final say on any Brexit deal.
Its timing - on March 23 - follows suggestions that a deal may not be agreed until the eleventh hour. Britain is due to leave on March 29.
More than 700,000 people took part in the previous People's Vote march in the capital in October last year.
Pro-Remain MPs from across the Commons welcomed the announcement, with Tory former minister Anna Soubry saying there will be "nowhere for any MP to hide" come the final week of March.
She said: "There is now a real danger that this is going to go right down to the wire. The Prime Minister appears intent on holding the long-awaited meaningful vote as late as possible, in the hope of pressuring MPs into backing what they know is a bad deal.
"And Jeremy Corbyn appears happy to let the clock run down, rather than tabling Labour's proposals or backing a People's Vote.
"But come the final week of March there will be nowhere for any MP to hide, which is why this march could be of historic significance. Parliament will need a way out, and the demand will be loud and clear: put short term party politics aside, put Britain's national interest first. Put it to the people."
It has been backed by Liberal Democrat leader Sir Vince Cable, who predicted "hundreds of thousands" of people would take to the streets, as well as SNP Westminster leader Ian Blackford and Green MP Caroline Lucas.
The announcement of the march followed the collapse of airline Flybmi on Saturday night. The company blamed "Brexit uncertainty".
Additional reporting by Press Association.
