British experts have called for tougher measures to improve the safety of clinical trials, including more stringent criteria for testing new drugs in humans, following a disastrous trial in which six men fell seriously ill.

The 19-member expert group was set up following Britain’s worst-ever clinical trial, the Northwick drug trial in March, in which six previously healthy men fell ill after participating in the first human tests of the new drug TGN1412, a genetically engineered antibody designed to boost the immune system.