Officers will have to deal with three protests by left-wing groups, including an event to "celebrate" the death of Baroness Thatcher in Trafalgar Square, as 50,000 football fans head into central London following the FA Cup semi-final between Millwall and Wigan.
Fans from Millwall have threatened to confront the anti-Thatcher protesters. The public have been warned to avoid central London.
Tomorrow night thousands have vowed to hold a party to celebrate the death of Baroness Thatcher in Trafalgar Square.
On the same day, UK Uncut, the anti-austerity protest group, have promised to hold a day of "civil disobedience" in protest to reforms to welfare, in which they will "evict" the "architects of austerity". It could mean the homes of Cabinet ministers are targeted.
And separately, the TUC is leading a march from 11am of "one thousand mothers" against benefit cuts in Tottenham - the scene of the worst disorder in London eighteen months ago.
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On Saturday night, 50,000 fans from Millwall and Wigan are due to convene on Wembley, north west London, for the FA Cup Semi Final.
Tensions between fans are likely to be running high after debates over whether a minute's silence should be held this Saturday, which is also the anniversary of the Hillsborough disaster.
Supporters will be making their way back through the capital after the final whistle has blown 7pm. Millwall's home is in south east London, while Wigan fans are likely to head towards Euston station.
At the same time, left-wing protestors are expected to be in Trafalgar Square, the scene of the worst of the poll tax rioting, in a "celebration" of Baroness Thatcher's death from 6pm. The event, billed as "the party of a lifetime", is thought to have been planned by anarchist groups for some years, having been pencilled in for 'the Saturday after Thatcher's dies'.
It is feared the two groups could clash.
Richard Tracey, a Greater London Assembly member who served as the Sports Minister in Lady Thatcher’s government, has warned members of the public to stay away from central London as it could descend into “chaos”.
He said: “Whenever any of these large demonstrations and marches are on it is always better for the public to keep very clear, because they can get nasty.”
Mr Tracey, who dealt with hooliganism during his time in Parliament, said that they combination of events was “very unfortunate” for the police who were already stretched dealing with the FA cup semi final.
The former Conservative MP, who said he was “very much against” the anti-Thatcher protests, said: “There is always the chance that this could cause chaos if one of the events runs into the other.
"Who knows what could happen as they all seem to get rather tribal.”
Football fans have warned of a confrontation on social media.
One Millwall fan with the Twitter handle 'Ricky MFC Mitchell' said: "To all you p----- protesting on Sat at Trafalgar sq about thatcher, be warned Millwall in town and in force, expect abuse from me #Millwall".
Another user wrote: "The commies are having a party to celebrate Thatcher dying at Trafalgar Sq Saturday. 30k Millwall fans will be about too in London that day."
Scotland Yard have said that they are monitoring social network sites, but added that they will have an "appropriate number of officers" on duty.
They already have an policing plan in place for both the FA Cup game and the Trafalgar Square demonstration, but it is unclear whether they have made allowances for the two crowds meeting and the prospect of officers being diverted by UK Uncut.
They have been frustrated by the anti-Thatcher groups' refusal to reveal all their plans.
During the day, hundreds of UK Uncut activists will launch a fresh campaign of civil disobedience in protest at the Government's controversial welfare changes.
The direct action group said it will hold events in central London to bring the impact of the cuts home to "millionaire misery makers" and highlight the effect of the bedroom tax and the cuts to benefits.
Rachel Johnson, a UK Uncut activist, said: "This government is turning Margaret Thatcher's wildest dreams into a nightmarish reality for ordinary people.”
The exact locations of the protests will not be revealed until tomorrow. However, it called on the public to target their "local millionaire misery maker". The group has publicly distanced itself from Trafalgar Square party.
Professor Simon Holdaway, a policing expert from Sheffield University, says tomorrow presents police with a demanding “jigsaw puzzle” which will stretch resources.
If any trouble flares, it will be a bad omen for Wednesday’s funeral, for which emotions are already running high, Professor Holdaway said.
London Mayor Boris Johnson has said that the Metropolitan Police are prepared for rioting.
He said the public is entitled to protest but added: “What they can’t do is, I think, is use the death of an elderly person to begin riot or affray or that sort of thing. So we’re getting ready for all that.”