Rock star Brian May will lead a rally against planned badger culls, due to begin from this weekend in an effort to tackle bovine TB.
The Queen guitarist, a long-time campaigner against the plan, will be joined by TV naturalist Bill Oddie as they lead a march through Westminster.
Organisers say they expect thousands to join them, all wearing badger masks, in an effort to demonstrate their opposition to the culls, the pilots for which are in west Gloucestershire and west Somerset.
Some 5,000 badgers are set to be killed in the two south west regions, with policing costs expected to reach £4 million to cope with potential disruption from activists.
Police last night said they were "prepared" for any disruption and protests.
The pilot culls aim to ensure free-running badgers can be killed humanely, with marksmen observed by independent experts to check they are killing the protected animal swiftly, and post-mortem examinations carried out to assess speed of death.
The pilots will also assess whether sufficient badgers can be killed in an area to have an effect in reducing TB in cattle, following a long-term study which found that culling 70% of badgers in an area could reduce the disease in herds by 16%.
If successful, the Government plans to roll out culling more widely in hot spots for the disease, which can be transmitted from badgers to livestock and between cattle. The costs of the cull will be borne by farmers.
But experts, including scientists behind the long-term trial, have raised concerns that the policy will have "unimpressive" results in reducing TB and suggested that it does not make economic sense.
The Government said the cull is necessary as part of efforts to stop increasing outbreaks of TB in dairy and beef herds, which saw 28,000 cattle slaughtered in England last year.
Without action, infection and costs would continue to soar, officials said.
Farming Minister David Heath said: "Nobody wants to kill badgers but the scientific evidence and experience of countries tells us that we will not get on top of Bovine TB without addressing infection in wildlife as well as cattle."
But shadow environment secretary Mary Creagh said: "Incompetent Defra ministers are pressing ahead with a badger cull despite scientists warning against this untested and risky approach."
A poll released yesterday reveals that the public is divided on the issue of culling, with around a third (34%) opposing the policy, and almost as many (29%) backing it. The remainder of those questioned did not know or had no strong views on a cull.
The British Veterinary Association, which is supporting the cull, urged protesters not to hinder the pilot schemes, so information could be gathered by independent experts to assess if shooting free-running badgers could be done humanely.
But Philip Mansbridge, chief executive of animal charity Care for the Wild, said: "The badger cull has no scientific, economic or animal welfare justification."
Avon and Somerset police assistant chief constable John Long said officers had long been "preparing to respond to any criminality or public disorder associated with the cull" since it was announced.
He said: "It is possible that the cull will attract protests and we respect people's right to protest against the action.
"We will facilitate safe, peaceful and lawful protests, as we have done with other protests, and would appeal for anyone intending to hold a demonstration to contact and work with us."
Superintendent Jim McCarthy of Gloucestershire Constabulary said: "Policing will be neutral and independent of any cull.
"We will deliver our statutory responsibilities which include dealing with any incidents of crime and disorder and ensuring that anyone who wishes to protest peacefully and lawfully is able to do so."