Police forces in England and Wales are on standby for what could be one of the biggest public protests in British history, the anti-Brexit march due to take place in central London on Saturday 19 October.

As MPs gather in the House of Commons for an emergency weekend sitting to discuss Brexit, more than a million people are expected to mass outside parliament for a People’s Vote march, while Extinction Rebellion climate campaigners launch the finale to a near fortnight of continuous protest.

Scotland Yard confirmed it was expecting a huge event and was liaising with the National Police Coordination Centre (NPoCC), which is responsible for the deployment of officers from across the UK to assist during large-scale events.

Deputy assistant commissioner Laurence Taylor, who is in charge of policing Saturday’s march, said: “We have considered what the event may entail and we will continue to monitor the resource level that we have. UK policing, let alone the Met, has very significant capacity and capability and if we need to draw on that, we will certainly do.”

Tom Baldwin, director of communications for People’s Vote, said that despite the special parliamentary sitting, the Met had signalled it would allow the march to Parliament Square, where Extinction Rebellion protesters are camped.

Talks over which group controls Parliament Square on the actual day indicate that Extinction Rebellion is likely to surrender its prime spot to accommodate the anti-Brexit protest, which could form the biggest public rally Britain has ever witnessed.

To date, the two largest public protests have been the Iraq war rally in 2003 and the last People’s Vote march held six months ago, which both drew more than a million people.

Baldwin added: “It does look like it’s going to be a very, very large event, without any doubt one of the largest protests this country has ever seen.”

For next weekend’s People’s Vote march, its third in the capital, 172 coaches have so far been booked from across the country, compared to 130 last time.

The number of individuals who have signed up to say they will attend the latest march is also already significantly higher. A campaign to raise funds for Saturday’s event reached its target of £500,000 with a week to spare.

Baldwin added: “Boris Johnson wants to run a campaign of the people versus the politicians. On Saturday you’re going to get politicians like Boris Johnson sitting inside the Houses of Parliament trying to force a form of Brexit on the British people and the people will be outside parliament demanding a final say.”

It is not yet apparent what form the Extinction Rebellion protest on 19 October will take, other than that it is scheduled to be the climax of 13 days of protest that have so far seen more than 1,100 people arrested since they began last Monday.

The rate of arrest – described by a spokesperson for Extinction Rebellion as an “astonishing number” – has even prompted speculation that the group might struggle to fulfil its protests for another week.

“We are still assessing what [the October 19 policing plan] is going to look like and how that works in conjunction with any Extinction Rebellion protest, if indeed the Extinction Rebellion protest is still ongoing,” said Taylor.