The protesters had broken away from another, bigger, march against US involvement in Vietnam but were confronted by a wall of police.

The breakaway group, led by the Maoist Britain-Vietnam Solidarity Front was almost thwarted by the march organisers who were aware of the plan and feared violence would erupt.

Once in Grovesnor Square the protesters formed a human chain and charged at the police wall but failed to break through and, after three hours of stalemate, they all dispersed.

Petition to Downing Street

In the streets surrounding the square fireworks and other missiles were thrown but no injuries were caused and police considered them to be isolated incidents.

The rest of the march, organised by the Vietnam Solidarity Campaign (VSC), continued peacefully to Hyde Park.

At Downing Street, Tariq Ali of the VSC, handed in a petition, signed by 75,000 to ask the government to stop supporting the US in its war against Vietnam.

The Home Secretary, James Callaghan, praised the demonstration saying "self-control was shown by the mass of the demonstrators".

He also praised the discipline and restraint shown by police.

"I doubt if this kind of demonstration could have taken place so peacefully in any other part of the world," he said.

Security for the march was high. A thousand-strong team of police was stationed outside the US Embassy and policemen lined the route of the march with back-up following in coaches.

The turnout for the march was around 25,000, half the number predicted by police and organisers.

But, far from being disappointed at the low turnout Mr Ali said; "This is not the end. This is the beginning of the campaign."

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