(Bloomberg) -- Follow @Brexit on Twitter, join our Facebook group and sign up to our Brexit Bulletin.

Thousands of protesters joined by senior politicians rallied in central London on Saturday to demand a second referendum on the U.K.’s exit from the European Union.

The deputy leader of the opposition Labour Party, Tom Watson, will be at the demonstration to promise he will back Theresa May’s twice-defeated political deal on the condition that she gives the public a vote on the accord.

The “Put it to the People March” was planned by the People’s Vote campaign, which demands a ballot on May’s deal. Marchers will walk through central London then congregate outside the Houses of Parliament to hear speeches from Watson as well as the Labour mayor of London, Sadiq Khan, and Scottish First Minister Nicola Sturgeon.

Watson’s pledge to back May goes further than Labour leader Jeremy Corbyn’s offer. Corbyn has proposed letting May’s deal pass in return for a second referendum, but only by abstaining, a condition which would require she muster greater support from her own divided party. Corbyn remains wary of alienating the sizeable proportion of Brexit-supporting Labour voters.

“If it was 52-48 percent again, I don’t think I could go along with that at all,” said marcher Katie Overstall, 27, when asked about Watson’s proposed public vote. “It would have to be a more significant majority.”

The march follows a tumultuous week for May. The premier had sought a three-month extension from the EU, but got only a two-week delay to April 12. If lawmakers approve her deal on a third attempt, the U.K. will have until May 22 to negotiate an orderly exit. There’s no guarantee May can bring the agreement to the House of Commons for a third vote, after it was blocked in principle by Speaker John Bercow.

Read a QuickTake on What You Need to Know as the Brexit Deadline Shifts

A similar protest in October drew an estimated 700,000 people. Saturday’s marchers will be accompanied by live performances from noted U.K. musicians including DJ Fatboy Slim.

Separately, an online petition seeking to stop Brexit by revoking the Article 50 notification collected more than 4.28 million people by midday Saturday, the most names ever collected in a public campaign.

The previous record for an online drive was 4.15 million names in 2016 on a proposal to hold a second Brexit referendum, according to the Parliament website.

When attendees Susanna Macintyre, 32, and Jessie James, 33, were asked if they were stockpiling any items ahead of Brexit, they answered “common sense” and “hope.”

To contact the reporters on this story: Thomas Seal in London at tseal@bloomberg.net;Lucca de Paoli in London at gdepaoli1@bloomberg.net

To contact the editors responsible for this story: Rebecca Penty at rpenty@bloomberg.net, Steve Geimann, James Amott

©2019 Bloomberg L.P.