By Emma Griffiths
BBC News Online, London
Policing last year's demonstration cost nearly £1.8m
Despite months of planning, police are still making last-minute changes to preparations for May Day.
The number of officers on duty this Thursday has been increased by a third, to 4,000, in the light of new information received by police chiefs.
An anarchists' website has published the names of 60 offices in central London which could be targeted on the day.
Although police stress that the majority of the thousands of protesters who head to central London are there for legitimate demonstrations - they have spent months preparing for the worst.
"It is difficult to plan because, if the people involved do not cooperate, then we don't have any estimates of numbers or locations, " said Deputy Assistant Commander Andy Trotter, who is in charge of the police operation this year.
"We have just upped our numbers to 4,000 because of concerns about the number of premises that might be targeted."
Our feeling is it will be the standard anti-capitalism protests and there will be an element about oil and armament production
Deputy Assistant Commander Andy Trotter
Ever since Winston Churchill's statute was defaced and a McDonalds branch vandalised during the chaotic protests of May Day 2000, the Met has been under pressure to prevent a repeat of the violence.
"I think people were shocked about the damage to national monuments and were surprised that 1 May, a day of workers' celebration across the world, was used to damage memorials and attack police officers," said Mr Trotter.
"As a result we had to increase the numbers of officers and change our tactics to deal with that."
By 2001 police were invoking special powers allowing riot officers to hem in thousands of protesters and aggrieved bystanders in Oxford Circus for eight hours.
Even last year's relatively peaceful May Day Monopoly demonstrations ended in a stand-off between activists and officers in Soho's Old Compton Street.
Troublemakers have been known to change their own tactics - last year they kept moving around the West End in small groups to prevent being hemmed in by riot police.
May Day map of London
Events, locations and times
But although police say rioters are not great organisers, they are not taking any chances.
Some officers will be patrolling the streets while others watch for troublemakers from mobile CCTV vans and helicopters.
'Reserve' groups will also be on standby to respond to events as they occur.
Demonstrations are expected in the City, the West End, Oxford Circus, Piccadilly and Park Lane.
Police are currently expecting smaller 'desegregated' groups of protesters but say there is no definite theme.
"Our feeling is it will be the standard anti-capitalism protests and there will be an element about oil and armament production," said Mr Trotter.
May Day is not the Met's biggest challenge of the year.
Last year the price of policing the event (£1.8m) was dwarfed by the Notting Hill Carnival's £5.4m cost to the police purse.
The force says it deals with 3,500 public order events each year and is ready for whatever May Day has to offer.
But while it is gearing up for a "difficult and challenging day", Mr Trotter says they will be supporting the majority of demonstrators who come for a legitimate day of peaceful protest.
"Anyone who was here for the Stop the War march or the Countryside Alliance could see that hundreds of thousands of people could express their views with the full involvement of the police," he said.