Image copyright Getty Images Image caption Sir Billy Connolly says having the disease is the first thing he thinks about every day

Sir Billy Connolly has put himself forward to become a stem cell research "guinea pig" as part of efforts to find a cure for Parkinson's disease.

The Glasgow-born comedian was diagnosed with the illness five years ago.

He said he has been in touch with scientists at Harvard University in Massachusetts whose stem cell institute is a key leader in research into Parkinson's.

His comments come in a book being serialised in a Sunday newspaper.

He said having Parkinson's is the first thing he thinks about every day and that the hardest part of it is "coming to grips with the fact that it's never going to go away".

In the book, serialised in the Mail on Sunday, the 75-year-old said: "I've spoken to guys working on it at Harvard and told them I'll be a guinea pig for them.

"I think they are going to take me up on that."

Sir Billy was diagnosed with prostate cancer - for which he had successful surgery - in the same week he was told he had Parkinson's in 2013.