Police are investigating claims an officer assaulted a former middleweight boxing champion at Hackney Carnival last month.

"Method man" Jason Matthews, 49, believes an officer "targeted" him because of the clothes he was wearing and his youthful appearance. "They thought I was young - I'm thinking to myself: 'Is this what police are doing to young people?'" he said.

He told the Gazette what happened as he entered Hackney Carnival. "People [were] going in both ends so I went through the exit sign - I didn't know it was an exit.

"Someone grabbed my clothes and started pulling me back so I pulled my arm away - it was a policeman. I said: 'Why you pulling my clothes for?' He's come round the other side - where I was - and he pushed me back to the fence and grabbed me by the throat."

He saw the officer again an hour and a half later and attempted to speak to him, but says was "roughed up" for the second time.

"He rushed me again," Jason said, "threw me onto the emergency ambulance. Now I'm spreadeagle on the van standing up, and he proceeds to punch my arm about 10 times - remember I'm still calm."

Jason said the officer asked for his phone and alleges he continued to punch him until he handed it over. Jason told the Gazette the officer then said he believed Jason had a weapon and threw him to the floor.

All officers found on him was some money and keys, and he was not arrested.

A crowd gathered as Jason was being searched. One onlooker filmed the incident and a man can be heard saying: "The man has done nothing." On video, during the search, Jason is clearly calm and compliant with officers. He believes the officer's behaviour changed when he realised Jason was older than first thought.

The commonwealth and world middleweight champion, who represented Hackney in the 1990s, had worn a black hoodie and sunglasses to the carnival to protect himself from the sun after getting sun stroke at Notting Hill Carnival two weeks earlier.

He has complained to both the Independent Office for Police Conduct (IOPC) and the Met directly. Scotland Yard did not respond to the Gazette's requests for comment.

Darren Ashwood was at Hackney Carnival and filmed the video showing police officers searching Jason.