The risks of the drug involved in the clinical trial which went disastrously wrong in Britain have been known since 2002.

A study published in the specialist magazine Clinical Immunology four years ago revealed that the medicine concerned, TGN1412, under development for treating leukemia and multiple sclerosis, could attack human tissue, the German daily Rheinische Post reported Saturday.

Two men remained critically ill and four in serious condition but conscious late Friday in a north London hospital after having an immediate, violent reaction to taking the drug.

German doctor Michael Stoeter, a member of the Berlin ethical commission, told the paper it was possible the young men who tested the drug were suffering from the secondary effects which scientists had warned about in the study.

"The fact that there was organ failure would appear to indicate that the drug attacked their tissue."

The six paid volunteers, all young and in good health, were the first human beings to be given the drug being developed by the German company TeGenero during a clinical trial operated by Paraxel, a US drug research company.