The mother of an 18-year-old Norfolk musician killed by a heroin overdose has warned of the dangers of 'legal highs' following the inquest into his death.

Freddy McConnel, who grew up in Billingford, was found dead at his London flat in May after his parents alerted a family friend and police when he failed to answer phone calls, Westminster Coroner's Court heard.

The former Gresham's School pupil appeared on Junior Mastermind aged 11 and had a promising future as a musician but had struggled with drugs in the years running up to his death.

And it was after the inquest that his mother, Country Life cartoonist Annie Tempest, warned of the dangers of 'legal highs', which she claimed her son had started using when he was aged just seven.

Ms Tempest said: 'Do not for a minute think that legal highs are safe. Freddy's diaries state clearly that he knew his downward spiral started with what was then a 'legal high', mephedrone. It was the gateway to his ultimate death.'

The inquest heard that Mr McConnel, who had become close friends with Peaches Geldof and 'idolised' controversial rock star Pete Doherty, had an IQ of 144 and was a member of Mensa.

Earlier this year, his father, composer James McConnel, told the EDP of a son who had great musical talent, and had written 'very, very accomplished' songs before performing his own music in venues across London at the age of 16.

However, Mr McConnel, who lives in the Holt area, said that the teenager changed as he started to experiment with drugs at high school, where he was suspended twice.

And it was just a few years later he was taking up to 30 grammes of mephedrone – also known as meow meow and a legal high until last year – and went on to inject up to a gramme of heroin every day, the inquest heard.

Coroner's officer Deborah Plant told the inquest: 'Tragically, Freddy had his demons and what had begun as experimentation with drugs gradually morphed into the full-on disease of addiction which, although he fought it, gradually defeated him.'

He had spent three months in the Priory rehab clinic in Essex last year and further time in a specialist clinic in South Africa, she added.

Although he had been suffering from depression and anxiety on his return, he was 'looking forward to recovering from his addiction', psychiatrist Mike McPhillips said in a report read at the inquest.

PC Gavin Thomas said he had to force entry to Freddy's flat in Winfield House, Vicarage Lane, Battersea, at about 10pm on May 28, after he and other officers got no response.

'It was deemed that we would go in through the sash window,' he said, adding that the 'deceased was there on the bed, lying face down'.

Drug paraphernalia, including syringes and a spoon, were close by, he added.

A post-mortem examination found toxic levels of morphine in his bloodstream.

Coroner Fiona Wilcox recorded a verdict of death by non-dependent drug abuse.

'This level is in the potentially fatal range,' she said.

'I am satisfied that it has caused his death, but I am also satisfied that he did not intend to take his own life.'

His father has previously criticised Doherty from glamorising drug use and said that he plans to continue editing and re-mixing his son's songs, including the 20 they made together.

He and Ms Tempest, who separated in 2006, are also looking at compiling his writing, which took the form of songs, poetry and diaries, into a book.

In a joint statement following the hearing, they said: 'Freddy's death was, of course, a tragic waste of a young life.

'But as his parents we can only hope that the moderate publicity it has received may help to bring attention to bear, not only on the dangers of drugs but on those who publicise and glorify their use.'

john.owens@archant.co.uk