The 78-year-old comedian, also known as The Big Yin, was diagnosed with Parkinson’s disease in 2013 and retired from live performances five years later.

But he has continued to record programmes and make TV appearances.

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The Scottish star appeared on the Graham Norton Show via video-link from Florida, where he lives, to talk about his new autobiography, Windswept & Interesting.

He told Norton: “I have lost the ability to write, and it breaks my heart as I used to love writing letters to people.

“My writing went down the Swanee and is totally illegible, so I had to find a way to record everything, but then the recorder didn’t understand my accent so it kept collapsing and my family would have to sort it – it was a club effort!”

Explaining the title of the book, he said: “The rules of being ‘windswept and interesting’ are doing as you please and not taking lessons from anyone.”

Sir Billy gave an update about living with Parkinson’s and said he has “good days and bad days”.

“It’s creeping up on me and it never let’s go. I walk like a drunk man and have to have help. So, life is different, but it is good,” he said.

Other guests on the show include Doctor Who star Jodie Whittaker, Olympic diver Tom Daley, actress Dame Eileen Atkins, and comedian and writer Sir Lenny Henry, with a musical performance from Coldplay.

Whittaker, 39, said in July that she would be leaving the sci-fi drama after taking over the Tardis in 2017 as the first female Doctor.

Asked about her forthcoming final series, she told Norton: “I’m not allowed to tell you anything, but I can say the first episode is out on Halloween and it is a six-episode story arc – it’s like a six-hour film and it is amazing.”

The actress will make her exit from the BBC programme in a trio of specials next year.

Whittaker said she does not know who the new Doctor is, and that scenes have been filmed but “the new Doctor wasn’t there”.

“I wasn’t there for Peter (Capaldi), and I only met him months later when I passed him in the street!” she added.

It’s A Sin star and singer Olly Alexander and actress Michaela Coel have been mentioned as favourites to replace Whittaker, but the BBC has not made an official announcement.

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Sir Lenny Henry spoke about his debut children’s book, The Boy With Wings, and described it as his “lockdown project”.

The 63-year-old said: “It’s a sort of superhero origins story – basically, I opened my head and poured out everything I remembered about comics. There is a lot of me in the book – I was bullied at school, and I wish I had those superpowers.”

The Graham Norton Show airs on BBC One at 10.35pm on Friday and is also available on BBC iPlayer