The Government's drug watchdog today criticised the firm behind a disastrous drug trial which left six men seriously ill.

Research firm Parexel failed to follow some correct procedures and made errors over contracts and patient records, the Medicines and Healthcare products Regulatory Agency (MHRA) said in its final report into the incident earlier this year.

But, it said, the adverse reaction seen in the men was most likely down to an "unpredicted biological action of the drug in humans".

That conclusion is the same one the MHRA came to in its previous interim report.

In the report, the MHRA outlines an inspection of Parexel carried out after it suspended the trial when the men fell ill in March.

All six previously healthy men suffered multiple organ failure after being given TGN1412, which is designed to treat rheumatoid arthritis, leukaemia and multiple sclerosis.

They were placed in intensive care and one sufferer was described as looking like "The Elephant Man".

The report said Parexel, which is based at Northwick Park Hospital in north west London, had "failed to complete the full medical background of a trial subject in writing".

One investigator had not updated records after a verbal consultation with one of the volunteers, it said.

The placebo volunteers were also allowed to leave the premises "before appropriate checks were undertaken to confirm that they were the two subjects that had received the placebo", it added.

This should have been done, despite the fact that events suggested they were the ones taking the placebo, the MHRA said.

Furthermore, the bank screening physician - the doctor who screens the volunteers before they enter a trial - did not have a contract.

The report said: "Having interviewed the bank screening physician as part of their inspection, MHRA inspectors were not satisfied that the individual had adequate training and experience for their role."

There was also no "formal system" in place for 24-hour medical cover and no contract in place between manufacturer TeGenero and Parexel, although one was subsequently issued, it said.