It was a mistake to allow Chinese secret police to guard the Olympic torch during its London relay, Mayor Ken Livingstone has admitted.

“It was wrong and should not have happened,” he told a BBC London debate.

Police said the guards got in the way of officers trying to restore calm during the 6 April procession.

At the Stratford debate Tory mayoral candidate Boris Johnson admitted he had underestimated the cost of putting conductors back on London buses.

Meanwhile Liberal Democrat candidate Brian Paddick said that if he were elected for mayor he would advertise for his advisers, rather than appoint them.

‘Unacceptable’

The three main mayoral candidates took part in the debate, to be broadcast on Tuesday.

When asked if he knew in advance that the Olympic torch guards were members of China’s military secret police, Mr Livingstone admitted that he did not.

“Had I known, I would have said it was unacceptable,” Mr Livingstone said.

“We are not involved in the running of the Olympics during the election campaign.”

Metropolitan police criticised the blue-suited guards as scuffles broke out between police and anti-China protesters.

Lord Coe, head of the London 2012 Olympics organising committee, described the guards as “thugs” who tried to push him out of the way of the procession.

Meanwhile Mr Johnson admitted his plan to reintroduce conductors to London buses would be three times the £8m he stated in March.

“It’s true that if you have three shifts (of conductors) it goes up,” he said.

“Nevertheless I think it is a price that Londoners would think would be worth paying.”

On Tuesday Mr Johnson told BBC London that the cost of implementing his plan to replace bendy buses with new Routemaster buses would be “around £100m”.

This would cost the same as Mr Livingstone’s plan to buy 500 “green” hybrid buses, Mr Johnson said.

During Monday’s public debate Mr Johnson refused to name the senior team of advisors he planned to use if he became mayor.

But Mr Paddick said he would advertise for advisors if he won the 1 May election.

“We will select objectively against published criteria so that we get the best people for London,” Mr Paddick said.

Indicating at his rival candidates, he added: “Not his mates, and not his mates.”

London Decides - The Mayoral Debate will be broadcast on BBC One in the London region at 2235 BST on Tuesday.