A participant in the drugs trial that left six people critically ill said doctors were convinced that he would not live. Ryan Wilson, 20, took part in the "elephant man" trials that caused organ failure in volunteers who were testing a potential treatment for rheumatoid arthritis.

The plumber, who left hospital yesterday in a wheelchair after "four months of hell", will lose all of his toes and part of three of his fingers as a result of the side-effects of the drugs. After suffering heart, liver and kidney failure, he still faces uncertainty as to whether his immune system will recover.

"Every doctor that was there said I didn't think you'd live, and most of the nurses said they didn't think I'd live," he said. "They had a look of amazement on their faces, they thought I was going to die, and I didn't."

In an interview with BBC's Six O'Clock News, Mr Wilson said: "There are a few parts of the immune system that are not right and they don't know if they will get back to normal, level off or decrease even more. It is hard to tell." He now faces further surgery so that he can walk again. "At the moment my goal is to have my operation, come through it successfully and walk," he said. "Once I have surgery, it [walking] will depend on how long I take to do it - it could be a month, it just depends on determination."

In March, Mr Wilson took part in the Tegenero clinical drug trial for TGN1412, which was hoped to treat leukaemia and multiple sclerosis as well as arthritis, to pay for driving lessons. But soon after being injected with the drug, for which volunteers were paid £2,000, their heads and bodies swelled. Mr Wilson said he would not be able to return to plumbing because of his limited dexterity.

He added: "There is no time to be weak in a moment like this. I'm not taking any plaudits for it, because I think most people would do the same thing."

Four of the men recovered and were discharged but Mr Wilson and Mohamed Abdelhady remained in hospital. Mr Abdelhady, who was described as looking like the "elephant man" by his fiancée, Myfanwy Marshall, has since been discharged from hospital. Solicitors are negotiating compensation for the six men.