The world of medical research has been thrown into chaos after an inquiry into a drug trial that went wrong concluded the problems had occurred because of an unexpected pharmacological reaction in humans.

The trial of the drug, TG1412, carried out in a private testing facility at Northwick Park hospital, London, last month, left six human volunteers in intensive care fighting for their lives. All six experienced severe reactions within minutes of taking the drug including fever, swelling and vomiting.

The inquiry by the Medicines and Healthcare Products Regulatory Agency (MHRA), which is responsible for drug safety in Britain, found there was no human error involved in the manufacture, preparation or dose of the drug.

The solicitor for the two most seriously affected victims dismissed the findings last night as "totally inadequate and accused the MHRA of a "lack of transparency." Ann Alexander said the authority had failed to give details of the pre-clinical trials, about which there was conflicting information, and had failed to publish the protocol for the trial.

The shadow Health Secretary, Andrew Lansley, criticised the way the MHRA was "scrutinising its own actions". He said: "It is only right that an independent group is established to scrutinise the decisions which gave rise to the original clinical trial authorisation."

The interim inquiry findings will cast a pall over the development and testing of all drugs with a novel biological action in the UK. The MHRA announced a review of drug testing and said that no further trials of novel compounds targeted at the immune system would be authorised without external advice from experts.

The conclusion means that despite the stringent safety measures already in place which require new drugs to be tested in the laboratory, on human tissues and in animals for several years, they can still produce powerful effects in humans that cannot be predicted. Experts said that they feared the impact on the future of drug testing.

Professor Geoff Hale of the Therapeutic Antibody Centre at Oxford University, said: "I am worried that this will make it even more difficult for hospitals and charities and academics - the non-commercial sector - to do drug development."

TG1412, made by the German company TeGenero, was being developed as a treatment for immune disorders such as leukaemia, rheumatoid arthritis and multiple sclerosis.

Although it was given to the six human volunteers in a dose 500 times lower than that previously used on monkeys without ill effects, the drug triggered a life-threatening immune response in the volunteers. The tests were run by a US-based company Parexel.

The six volunteers, all men aged 19 to 40, were taken to Northwick Park Hospital within hours of the start of the trial on 13 March. Three weeks later one remains in hospital and the other five have been discharged. All are improving, according to the hospital.

Professor Kent Woods, the chief executive of the MHRA, which carried out the inquiry, said: "There was a powerful pharmacological action of this drug in man that was not detectable in tests on non-human primates at far higher doses. This raises very important questions about the pre-clinical testing of products of this kind."