A British newspaper on Sunday reported a claim that a fifth man had planned to take part in the suicide bombings of London's transit network a year ago, which killed 52 commuters and the four attackers.

The Sunday Times quoted an unidentified friend of bomber Shezad Tanweer who said he had learned after the attacks that a fifth man had admitted his intentions to his family and was talked out of joining the group on the morning of July 7.

A unit of London's Metropolitan police investigating the bombings was aware of the claims about the unidentified man, they have not interviewed him, the newspaper said.

Britain's Home Office, which is in charge of the police, said in a report published in May that there was no intelligence to indicate that a fifth bomber had been due to take part in the attacks.

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"The report said there was no evidence of a fifth bomber and we have no reason to believe there is a need to alter that view," a Home Office spokesman said on Sunday, on customary condition of anonymity.

Peter Clarke, head of anti-terrorist policing in London, has also previously discounted suggestions of a fifth bomber.

He said police were continuing to investigate whether any criminal charges could be brought against people who helped plan or finance the attacks, or who failed to inform police about them.

Suspicion that additional attackers could have been involved was raised when police discovered unused explosives in a car used by the gang and parked on the outskirts of London.

But officers said the devices, small bombs packed with nails, were likely intended to be used in the event the group was stopped before reaching London.