A 15-year-old boy was mugged, threatened with a knife and assaulted during a horrific gang attack in a Watford park yesterday afternoon.

The boy, from Middlesex, was walking near the Riverside Recreation Ground skate park with two female friends when he was set upon by a group of ten teenagers, shortly after 4pm.

He was assaulted by a number of youths, one of whom threatened him with a knife and demanded his Blackberry mobile phone.

The victim suffered cuts and bruising as a result of the incident but was not injured by the knife, Hertfordshire Constabulary has confirmed.

Officers say that the majority of the group were black and aged between 17 and 19. Two of the gang are thought to be white.

The victim was able to give a good description of two of his attackers. They are: a white man, about 6ft 1in tall, with a slim build and long sideburns. He was wearing a blue flat cap and casual clothes.

The other was a black youth, about 5ft 7ins tall, and of slim build. He wore a grey jumper and grey jogging bottoms.

On Friday, June 3, a 15-year-old girl was sexually assaulted by three black men in the park at about 11pm.

Residents later raised concerns about the level of antisocial behaviour and low-level crime in the skate park area – which is shielded from public view.

Chief Inspector John Dempsey-Brench, Watford’s most senior policeman, said the latest incident was being taken very seriously but stressed that knife-crime remained a very rare event in Watford.

He said: “This type of event is taken very seriously and we will work to catch those responsible – but this area is not a crime hotspot. It did not feature in our crime mapping statistics last year but we have had a couple of incidents there in quick succession.

“When we have a spike in activity like this we do put in additional resources to provide reassurance and prevent similar incidents happening again.”

Anyone with information is asked to call police on 0845 3300222, quoting crime reference C1/11/3658.