London police are bracing for protests at Margaret Thatcher's funeral on Wednesday, with opponents vowing to pelt her coffin with eggs, coal or milk if they can get close enough -- or simply turn their backs on the passing procession.

More than 800 people have pledged to attend an event called "Maggie's good riddance party", promising a "right jolly knees-up" outside St Paul's Cathedral -- where 2,000 global political leaders, celebrities and friends will be paying their respects to the former British prime minister.

"Let the world know the hypocrisy of a state-funded funeral for the person who influenced 30 years of cuts to state funding of welfare," the protest's Facebook page reads.

"If taxpayers are funding her funeral... we can at least get our money's worth."

The former Conservative Party leader's death has sparked furious debate in Britain over her legacy -- and over the decision to grant her a state-funded ceremonial funeral, which by some estimates will cost the taxpayer up to £10 million ($15 million, 12 million euros).

Her more radical critics, who accuse her of ruining millions of lives with her radical free-market reforms, greeted news of her death from a stroke last week with impromptu street parties.

Hundreds of people filled London's Trafalgar Square on Saturday, erected a giant effigy of her and shouted "Maggie, Maggie, Maggie! Dead, dead, dead!"

Scotland Yard has launched a massive security operation, fearing that protesters could attack the 1.9-kilometre (1.1 mile) route between parliament and St Paul's. Her coffin will be carried on a horse-drawn gun carriage through streets lined with military personnel.

Police have repeatedly asked demonstrators to give them advance notice of their plans, warning that anyone causing "harassment, alarm or distress" could be arrested.

Some protesters have vowed to pelt the coffin with eggs, while others have hinted at hurling coal -- a reminder of the bitter 1984-1985 miners' strike which Thatcher crushed, leading to the closure of dozens of mines and tens of thousands of job losses.

"Please remember your coal to throw at the cortege, it's what she would have wanted," one Twitter user posted.

Former miners were among those celebrating Thatcher's death at Trafalgar Square on Saturday -- and pubs in areas where the mines were shut down, from Wales to northern England, are expected to do brisk trade on Wednesday.

In London, some protesters suggested they may try to throw milk at Thatcher's coffin, a reference to her days as education minister when her decision to stop free milk for older school pupils earned her the nickname "Thatcher the milk snatcher".

Westminster City Council has nine "flushing machines" and 40 staff on standby to clear the streets of milk if necessary, a spokeswoman said.

But many of Thatcher's foes said that simply turning their backs as her coffin passes would send a more powerful message.

"If many people turn their backs it will be a deeply symbolic act," said Becca Blum, an environmental activist who said she had police permission for a peaceful protest outside the Royal Courts of Justice.

"We will show the world that Britain is not all united in grief," she wrote on her blog.

A Scotland Yard spokeswoman said an "appropriate" policing operation was in place for Wednesday.

She declined to say how many officers would be on the ground, adding that the force had been in contact with some protesters.

"We are hugely experienced in safely delivering high profile and ceremonial events in the capital," said Commander Christine Jones, who is leading the operation.

It is yet another large-scale operation for the London force after the wedding of Prince William and Kate Middleton in 2011, last summer's Olympic Games and Queen Elizabeth II's diamond jubilee celebrations.

St Paul's itself is no stranger to protests. Lying at the heart of London's financial district, it was home to anti-capitalist "Occupy" protesters for more than four months until their camp was evicted in February 2012.

Shopkeepers along the funeral procession route have been told to remove signs from the pavement, as well as any ladders or tools that could potentially be used as weapons.

"We're moderately concerned about it," said Stuart Dove, manager of George Attenborough and Son jeweller's on Fleet Street, near the cathedral.

"We might have to put our shutters down, depending on how big the crowd gets. It's a bit annoying for business, but I think it's important that London marks the occasion," he told AFP.