The father of a young man brutally mugged on Hampstead Heath says his son is "lucky to be alive" after being set upon and stabbed by three thieves.

The 22-year-old man was taking a walk on the Heath Extension on September 27 when he was attacked by three strangers at around midday.

He suffered multiple cuts to his arms, legs, head and neck, as well as bruising.

The thieves fled with his rucksack which contained just a tracksuit top, water bottle and mini blue tooth speaker.

"They will get away with it, get off scot free," said the victim's father, who asked that the family not be named.

"My son just went for a walk to get some fresh air as he hasn't been feeling too well. He was feeling dizzy and bowed down to be sick.

"He remembered a man asking him if he was okay and offering help but instead he grabbed his rucksack to steal it. My son's instinctive reaction was to hold on to it and a tug of war took place.

"Other guys joined in and one of them had a knife. It wasn't nice. He doesn't remember when they fled."

He said his son was wearing layers of clothing including a puffer jacket, and had a wallet in his trouser pocket which contained about nine cards.

"He got a lot of cuts on his arms, legs, head and his neck, none of them very deep or in need of stitching. They tried to stab his leg but the knife breached his wallet and three cards were destroyed.

"My wife and I are both very conscious that he was lucky with his injuries which could have been much worse."

He said his son is physically getting better but that he is getting flashbacks.

He asked that if anybody witnessed the mugging or has any footage that could help the police investigation to contact officers.

"I hope it doesn't happen to anyone else," he added.

The Met said it was called at 12.15pm on September 27 to reports that a man had been assaulted during a robbery in the vicinity of Hampstead Heath Extension and was treated for minor injuries. There have been no arrests.

Anyone with information should call police via 101 quoting reference CAD 2888/27Sep.