He's looking very gaunt and very thin - things aren't looking too good

Phil Day, spokesman

But doctors have now diagnosed an abscess at the base of the former body-builder's spine and are carrying out tests before operating.

The actor lost the use of his arm in February and was taken to hospital but had been recovering and regaining weight in recent weeks.

His spokesman Phil Day said today: "He's looking very gaunt and very thin. Things aren't looking too good."

Sci-fi conventions

He was taken to Mayday Hospital in Croydon, south London on Friday and has been confined to bed.

David Prowse appeared in the Green Cross Code adverts

Prowse has been walking with a stick after an operation two years ago left him with one leg shorter than the other.

The former Mr Universe contestant is still popular at science fiction conventions for his role as Darth Vader.

He is also well-known as the Green Cross Code Man for his appearances in 1970s public information films.

Mr Day said: "I spoke to him on Thursday and he told me he could not move and then he was taken to hospital the following day.

"The doctors found the abscess but obviously at the base of the spine there is concern because it's dangerously close to the vertebrae. He's going to be in hospital for quite some time."

It is believed the abscess was also the cause of his earlier problems.

Mr Day added: "At the moment they are taking samples to find out what it is made of before they can work out what to do."