Protesters from Aberystwyth to Aberdeen and from Penzance to Perth will travel to central London today for the biggest demonstration in Britain since the anti-Iraq war marches eight years ago.
Up to 250,000 people will take to the capital's streets to condemn the Coalition Government's programme of cuts.
The "March for the Alternative" has been organised by the TUC, but trade union activists will be joined by members of voluntary and community groups, churches and other religious organisations, as well as students protesting against tuition fee rises. Their numbers will be swelled by nurses, doctors, midwives and off-duty police officers angry about the cuts.
Eight hundred coaches and 10 special trains will bring the demonstrators to London, along with one man who has spent the week walking from Cardiff. More than 4,500 police officers and 1,000 stewards will marshal them on their three-mile route from the Embankment to Hyde Park, via Trafalgar Square.
Scotland Yard and the TUC have planned the demonstration and representatives from Liberty will monitor policing both on the ground and from Metropolitan Police headquarters. Officers have been accused of adopting strong-arm tactics in previous marches by resorting to the "kettling" of protesters – penning them in a confined space, sometimes for hours.
But the greatest worry for organisers is that the event will be hijacked by groups of anarchists and anti-capitalists intent on causing trouble. Police, who have been monitoring such groups on the internet, have advised shops and businesses along the route to ensure their doors are secure and their CCTV cameras are working.
The group UK Uncut is targeting banks and shops in Oxford Street and plans a "mass occupation of a top-secret target". Other activists are said to be planning to stop traffic with "flash mobs".
Andy Hayman, the former Assistant Commissioner of the Met, said: "There is strong intelligence extremist groups are planning illegal acts of violence...with the sole aim of disrupting a well-intended peaceful protest." Writing for the Policy Exchange think-tank, he said: "Unless the police become more proactive in disrupting the activists before the event, it will be impossible to ever stage a protest without it being infiltrated by extremist groups."
A TUC spokesman said: "We are aware of other stuff taking place. But we're very confident our event will be a peaceful, family event."
The rally in Hyde Park will be addressed by trade union chiefs and the Labour leader Ed Miliband, as well as non-political members of the public opposed to the cuts. They will argue that ministers are cutting too fast and too deep, jeopardising hundreds of thousands of jobs and hitting services.
Mr Miliband will tell the demonstrators they represent mainstream opinion in Britain, charging David Cameron and Nick Clegg with practising the "politics of division" by pushing through ideological Thatcher-style cuts.
"They're saying people in the public sector and people in the private sector should somehow be at odds," Mr Miliband will argue. "They're saying people on benefits should be resented by those in work. They're saying we should set North against South. We can't go back to that."
The TUC general secretary, Brendan Barber, who is overseeing the movement's largest demonstration for 25 years, challenged ministers to heed the protests and alter their "damaging" policies, which threaten more than 170,000 job losses in local government and another 50,000 across the public sector. He said: "The objective is to send a strong message to the Government through our unity and a huge turn-out. I want nothing to distract from that."
The Conservative MP Greg Hands said: "Mr Miliband and Mr Barber have a duty to ensure their march does not become a focus for disorder and law-breaking."