Detectives were today awaiting the results of forensic tests to help them trace a rogue batch of heroin thought to have claimed four lives.

The revealed that experts were analysing substances taken from the bodies of four Bradford users who died over a ten-day period.

It is hoped police can trace the batch - either contaminated or unusually pure - before any more deaths occur.

Police and drug agencies urged addicts to avoid injecting the drug and to seek professional help. Detective Inspector Gerry O'Shea, who is leading the investigation, said it was 'strongly suspected' that each person had taken heroin.

He appealed for dealers to dispose of any remaining substances - or face 'very serious' criminal charges if they supplied the deadly drug.

Det Insp O'Shea stressed: "The danger has not passed by any means. Users must realise they still face an enormous risk if they choose to take heroin." Within days, detectives should receive the results of laboratory tests.

The first death came on August 23 when the body of 23-year-old Stuart Finan was found at a house in Clayton. A week later a 23-year-old man was discovered dead in Ravenscliffe and the following day a 21-year-old died at Scholemoor. The last fatality came on September 1 when a 35-year-old man was found dead in the Little Horton area.

The Bradford Drugs and Alcohol Action Team said it was liaising with police over the precise causes of death and warned of the dangers of injecting heroin.

Alison Richards, the group's co-ordinator, said: "We would encourage any drug user to approach agencies such as the Bridge Project in Bradford and Project 6 in Keighley to get advice and help. Any drug user who wants help to stop using drugs can approach these, or their GP.

The Bridge Project is on (01274) 723863. Project 6 can be contacted on (01535) 610180.