Baton rounds and armoured vehicles will be available to police in London should trouble break out at a demonstration on Wednesday by thousands of students over fees and spending cuts, senior officers said on Monday.

Four thousand police will be on duty to try to prevent a repeat of the violence that marred student protests a year ago when demonstrators smashed their way into the Conservative Party headquarters in Westminster.

Students plan to march into the City of London but police have agreed their route will bypass St Paul's Cathedral where anti-capitalist protesters have set up camp.

Simon Pountain, the commander in charge of policing Wednesday's protest, said that baton rounds -- non-lethal rubber bullets -- would be used only in an emergency such as to rescue officers from attack.

If they're stuck and their lives are at risk, then I would use that to protect them, Pountain said.

The demonstration, which 10,000 students are expected to attend, is the biggest test for London's Metropolitan Police since rioting broke out in the capital in the summer.

Pountain said the number of police on duty was a reflection of the violence over the past year.

I have over 4,000 resources on this demonstration. A couple of years ago, a demonstration of 10,000 people would have attracted nowhere near that amount of resource.

I have a backdrop of the problems through the summer. I have a backdrop of the issues that occurred during the last student demonstrations, he added.

One anarchist group said they planned to take part in the protests.

This is our opportunity to join together with those who will not be governed by markets, dictated to by politicians, or accept the conditions being forced upon them, said an online posting from the N9 Anarchist bloc.

Let's make this a day the government will remember.

The tent camp, inspired by the Occupy Wall Street movement and construction of temporary grandstands for this weekend's Lord Mayor's Show, made it unsafe for protesters to march past St Paul's, Pountain said.

He expected many of the people from the St Paul's camp to join the student demonstration but said measures would be in place to prevent breakaway groups from trying to get close to the London Stock Exchange, the original target for the anti-capitalist protesters.

Police will have a senior officer on duty on the day to coordinate the use of containment measures should there be trouble.

The tactic, often referred to as kettling, has proved controversial at protests over the past year.

Containment is a lawful tactic for us to use and is valid but as a last resort, Pountain said.

(Additional reporting by Michael Holden; Editing by Steve Addison)