A top scientist has defended Britain's system of clinical testing after six men fell seriously ill during a London trial of an anti-inflammatory drug.
The six are being treated at Northwick Park hospital
Fertility expert Lord Robert Winston told the BBC he rejected claims that regulation was "weak and ramshackle".
Britain's system was among the "strongest and most carefully regulated" in the world, he said.
The six men have been in intensive care since falling ill on Monday. Two of them remain in a critical condition.
Doctors at Northwick Park Hospital in north-west London said the men had been given several blood transfusions to try to rid their bodies of toxins.
Four were said to be showing signs of improvement but doctors said it was still early days.
The men suffered multiple organ failure within hours of taking the drug TGN1412 during a trial at a research unit based at the hospital.
It was the first time the drug, designed to treat conditions such as rheumatoid arthritis, leukaemia and multiple sclerosis, had been tested on humans.
Lord Winston, professor of fertility studies at Imperial College London and vice-chairman of the Parliamentary Office for Science and Technology, told BBC Radio 4's The World Tonight Britain's system of clinical trials had "lots of safeguards".
Responding to a question by Labour MP Paul Flynn, he said: "I think it's really unfortunate that there might be given an impression that our very ethical drug industry is actually not working according to proper practice because I think on the whole it undoubtedly is."
He said he was concerned about growing resistance to animal testing in Britain and the effect this might be having on drugs trials.
He said: "I wonder really whether in fact there's increasing reluctance to do the preliminary trials on animals because of the difficulties generally in doing animal research.
"That I think is a disaster for humans."
American company Parexel, which ran the trial, said it had followed recommended guidelines.
TeGenero, which manufactures the anti-inflammatory drug, apologised to the sick men's families and said the medicine had showed no signs of problems in earlier tests.
The company's chief scientific officer, Thomas Hanke, said he and his colleagues were "devastated" by what had happened.
He said TGN1412 had been tested extensively in laboratories and on rabbits and monkeys for safety with no adverse effects and no drug-related deaths.
He added that the company's first concern now was making sure the patients got the best treatment possible and to support their families.
Scotland Yard said officers were talking to the Medicines and Healthcare products Regulatory Agency and doctors.
The MHRA is investigating whether the reaction suffered by the men was caused by a manufacturing problem, contamination, a dosing error or whether it was some "completely unanticipated side-effect of the drug in humans".