The Mayor of London Boris Johnson has accepted that the Met police may have shied away from investigating electoral malpractice in Tower Hamlets because the target would have been an ethnic minority population.

He was facing questions from the London Assembly when he was asked by Assembly Member Tony Arbour whether the inaction was due to the “Rotherham syndrome” – “where the police were reluctant to investigate because they believed that somehow or another that these complaints were against a particular section of the community”.

The mayor replied: “I’m afraid that must be the suspicion. I hope that nothing like this ever happens again and there will be free and fair elections on June 11.”

Mr Arbour pointed out that the Met had received complaints over a number of years from a number of reputable sources. These were not, he said “frivolous complaints”.

Mr Johnson said: “As soon as the news of the allegations of electoral fraud were raised in Tower Hamlets I did pick it up with the police and the message I got then was that there were a great many allegations against various parties but no single smoking gun on which they could launch a prosecution.

“There’s a certain difficulty for the police trying to overturn the will of the people. It certainly wouldn’t be my function as mayor to incite the police to overturn the result of the election.

“There has since been an election court and [High Court judge] Richard Mawrey has overturned the election and made some strong and interesting findings.”

Mr Abour added: “Mr Mawrey’s report he makes it clear that examples he has given are fireproof but he does say it is only by the smallest margin that the other matters which were raised – intimidation and things like that – he chose not to single out.”

Mr Johnson said: “The election commissioner upheld a number of allegations. It may be that criminal proceedings could be launched from those upheld allegations but I must stress that the level of proof required in the electoral court is lower than in a criminal court.

“What the police have told me so far is that they would find it difficult to frame charges. I think the matter is under consideration.”