A former public schoolboy died at a friend's 21st birthday party after snorting a powerful drug normally used as a horse tranquilliser.

Party-goers initially ignored Dean Coldwell, 21, as he lay unconscious on the floor after snorting ketamine, also known by users as K, Special K or Kit Kat, for the first time.

Lancing College old boy Mr Coldwell, of Tremains Lane, Horsted Keynes, near Haywards Heath, had taken nine times the maximum safe dose.

Former school friend Stuart Hall told an inquest yesterday how a group of friends had celebrated a 21st birthday at cafe in Wandsworth, London, on March 15.

The party then moved to Mr Hall's flat in Cupar Road, Battersea.

Mr Hall told Westminster Coroner's Court: "I saw Dean snort a line of ketamine. I went to the bathroom and Dean was there unconscious."

But his friends could not revive him.

He was taken to Chelsea and Westminster Hospital where he was pronounced dead.

A post-mortem examination revealed he was twice over the drink-driving limit and had taken a huge amount of ketamine, 3.6 mllllgrammes per litre of blood. It is only safe for human use between 0.1 and 0.4mg per litre.

Recording a verdict of death by non-dependent use of drugs, coroner Dr Paul Knapman said: "It would seem likely he was an unsophisticated user of drugs and this has caused his death."