If the estimate is correct, it would be the biggest march in the UK since the Iraq War protest in 2003.

Organisers of the anti-Brexit march through London on Saturday have said that as many one million people have taken to the streets for the People's Vote march to demand a second Brexit referendum. The numbers were provided by People's Vote UK, the organisers of the march on which protestors will travel from Park Lane to Parliament Square. A rally will be held at the finishing stop later in the day. https://twitter.com/peoplesvote_uk/status/1109461396213956610 A number of high profile celebrities and politicians joined the masses of people marching for a second Brexit vote. Scottish first minister Nicola Sturgeon travelled down to the capital to take part, as well as the likes of Tom Watson, Vince Cable, Caroline Lucas and Rosena Allin-Khan. https://twitter.com/richcooper/status/1109452241210089472 The march has gained significance against a backdrop of turmoil in the UK's Brexit negotiations and strategy. In recent days, that turmoil - which has seen prime minister Theresa May's Brexit deal rejected twice by parliament - has led to more than four million people signing an online petition which calls for the revocation of Article 50, the clause which Theresa May invoked on March 29, 2017, beginning the process of Brexit in earnest. The march comes a day after the Guardian published leaked government plans for a no deal Brexit, plans which highlighted the chaos which crashing out of the European Union would cause in the United Kingdom. According to the secret Cabinet Office documents, there will be a "critical three-month phase" during which "Operation Yellowhammer", the codename given by the Treasury for cross-government contingency planning for the possibility of a no deal Brexit. The documents also state that there will likely be likely to be "unforeseen issues and impacts" resulting from no deal. https://twitter.com/PoliticsJOE_UK/status/1109450359322411008