Richard Barnes, one of London mayor Boris Johnson’s deputies, is being investigated for allegedly making a racist joke about rioters.

According to the Daily Mirror, a City Hall worker complained after overhearing Mr Barnes say: “Why did police put Persil in the water cannons? To stop the colours running?”

Greater London Authority’s standards committee will investigate the alleged remarks, which were reported on August 15th.

Mr Barnes has denied being racist.

His spokesman said: “Richard works incredibly hard on behalf of all communities, regularly engaging and meeting with representatives

“It’s worth noting that Richard’s denial is around the allegation that he was being racist, not that he said the words or passed on the joke, which he was recounting with much disapproval.

“Also, it’s worth knowing that the monitoring officer is bound to investigate whether or not there has been a breach of code, that isn’t decided at this stage, and it could be concluded there has not been a breach.”

Mr Barnes, who is openly gay, is in charge of equality issues at the authority. In July, he was criticised for a remark about Irish builders.

He earns £106,000 as a deputy mayor and a Hillingdon councillor.