Dramatic video footage shows the moment a brave cyclist chased down three men who allegedly pushed another rider off his bike before stealing it.

Police have confirmed they are investigating the alleged attack in Leyton, east London, which saw the 53-year-old victim thrown off his bike and punched in the back of the head.

In the video, another cyclist's head-cam captures the aftermath of the assault on March 17.

The rider, 25-year-old Alex Sweeting, told the Standard he did not stop to think before giving chase and scaring off the attackers.

He said: "It was only when I stopped that I realised what I'd done.

"I didn't see it happen, but I saw this guy running along in cycling shoes, which I thought was a bit odd.

"I don't know if it's audible on the video, but I said 'have they taken your bike?' and he said yes. So I thought I'd ride off after them.

"I've got a camera on my helmet and I thought at the very least I might get a shot of them."

He continued: "I wasn't thinking much at the time. It was just: how can I get near them?

"For a split second I thought I might be able to kick them or push them.

"As you can see, when I caught up with them they dropped the bike and ran off."

The web developer from Barking, himself a keen cyclist, said the victim was "grateful" but annoyed the men managed to get away.

He added: "I actually got the camera for Christmas because of an incident with a car, so I'm really glad I got it. Hopefully it'll lead to some sort of prosecution or charge."

In the attack on Orient Way, police said one suspect "charged" at the victim to knock him off his bike, while another suspect punched him in the head as a third made off with the bike.

A spokesman said two unknown cyclists chased them down the road. The victim suffered mild injuries but declined medical attention.

Police said officers later searched the area but failed to locate the suspects after the attack last Tuesday at about 10pm.

The three men were reported to be between the ages of 18 and 25 and all about 5'8". Two of them were described as black, while the other was thought to be Asian, police said.

Anyone with information is asked to contact Waltham Forest police on 101 or Crimestoppers anonymously on 0800 555 111, quoting crime reference number 4905428/15.