Scotland Yard has dismissed suggestions from Ukip leader Gerard Batten that water cannon could be deployed at protests to “provoke Brexiteers”.
The Metropolitan Police, which does not own any of the machines, said reports it could use them at Brexit rallies were “baseless and false”.
Mr Batten is due to speak at a rally alongside ex-English Defence League chief Tommy Robinson against “Theresa May and her traitorous Tories” on Whitehall on Friday afternoon.
Westminster is expected to see mass protests and counter-protests on the day that Britain was scheduled to leave the EU.
Road closures may be enforced around the area, Transport for London warned.
Westminster Council said it is aware of up to 13 separate scheduled protests and the Metropolitan Police said “appropriate policing plans are in place”.
Here are some of the scheduled rallies:
4pm – Make Brexit Happen
Mr Batten, Mr Robinson and “other prominent Brexiteers” are due to speak on stage at a rally on Whitehall at around 4.30pm.
Mr Batten tweeted: “There are reports that water cannon may be deployed tomorrow in London, and that some of the police may try to aggregate and provoke Brexiteers.
“There is always the danger of provocateurs planted to cause trouble. I hope it is not true but I call on everyone present to be peaceful.”
4pm -Stand Up To Racism
The group said it will hold a “counter protest against the far right who are trying to capitalise on the Brexit crisis” and said it will directly oppose the Make Brexit Happen rally.
12pm – Fishing For Leave
Fishermen accompanied by a 32-foot trawler aboard a lorry will set off from Lincoln’s Inn and walk into Parliament Square at around noon escorted by a pipe band.
The group, which has the slogan “Yellow wellies not yellow vests”, said: “Our fishermen have been sold down the river by Theresa May”.
4pm – March To Leave.
The procession, which left Sunderland two weeks ago, is due to arrive at Parliament Square at around 4pm.
Former Ukip leader Nigel Farage, businessman and Wetherspoon founder Tim Martin and broadcaster Julia Hartley-Brewer will speak at the “Brexit Betrayal” rally.
Organisers have said “it is now clear the Westminster elite are preparing to betray the will of the people over Brexit”, adding: “Failing to deliver a true Brexit will permanently damage the British people’s faith in democracy.”
Westminster council said it was aware of expected rallies from groups including: the DFLA (Democratic Football Lads Alliance) Brexit Party; Stand up for Democracy; EU Leaving Party; March of Freedom; Proud British; A Night of Demonstration and Liberty; United Under Yellow; Rally to Rejoin the EU; Fridays for Future and Critical Mass.
The Metropolitan Police said “appropriate policing plans are in place” to cope with “a number of demonstrations and protests” on Friday.
A spokesman said: “We will always provide a proportionate policing plan to balance the right to peaceful protest, while ensuring that disruption to communities is kept to a minimum.
“To date, protests have been largely peaceful and we have no intelligence at this time to suggest that will change.
“We would like to reassure the public that officers will be ready to respond should any incidents or other spontaneous protests arise.”