POLICE have launched an assault investigation after a teenager had his forehead punctured by nails in a prank prompted by a TV stunt show.

And today it was revealed that the boy's horrified mother only learned of the incident when a picture of it was published as part of a Lancashire Evening Telegraph investigation into cult show Jackass.

The move comes after 10-year-old Joe Armstrong, of Tunnel Street, Darwen, was badly burned when another stunt went wrong.

The 13-year-old Darwen boy was pictured having his forehead pushed onto nails and punctured on a website set up by a Darwen teenager and spawned by the MTV programme, which has also been on Channel 4.

Detectives are in the preliminary stages of a criminal investigation after the mother alleged her son had been assaulted. Detectives spoke to the boy yesterday in a bid to discover more details, including when the incident took place. They believe more complaints could follow because of the numbers of children involved in the dangerous pranks.

Police said the first the mother knew that her son was involved was when his picture was on the front page of the Lancashire Evening Telegraph on Tuesday next to the headline 'Stop this Madness'.

Joe, a pupil at Tockholes Primary School, is recovering at Booth Hall Hospital in Manchester with burns to his chest and thighs. He will be scarred for life.

Acting Detective Superintendent Neil Smith said: "A boy aged 13 from Darwen was interviewed yesterday afternoon. His mother has made a formal complaint and we are conducting preliminary investigations into the allegation which we are taking seriously.

"The first the mum knew about it was through the photograph in the Telegraph. The complaint is of assault. Someone cannot consent to being assaulted."

Police are as yet unclear about what the boy told his mother about how he got the holes in his forehead.

MPs and Media watchdogs have called for Jackass, made in the USA, to be banned from UK screens after evidence of what the Darwen boys had been doing was revealed.

Michael Davies, 15, of Anchor Avenue, Darwen, had been videoing the group of youngsters jumping over fire for his Jackass-inspired website last week when Joe's clothing caught alight.

Michael said he was distraught about what happened to Joe and said he would close down his website Live Now Die Later as a result. And broadcaster Anne Diamond has now called for Jackass and similar shows to be banned when the case was featured on Channel 4's teatime show Richard and Judy last night.

She revealed that two of her four children had admitted to watching the Jackass show and that broadcasters failed to realise that youngsters -- including her own nine-year-old son -- could be prompted to try stunts, despite on-screen warnings.

Channel 4 and MTV, who screen Jackass, said the show was shown after the watershed with strenuous warnings to viewers not to repeat any of the stunts. Broadcasting watchdogs Ofcom, which took over responsibility for regulating TV programmes last year, has said it will consider what happened to Joe when drawing up new guidelines.