IN April ITV broadcast an affectionate tribute to the man forever known as the Big Yin.

The hour-long special, Billy Connolly and Me: A Celebration, featured celebrities – Judi Dench, Armando Iannucci, Eric Idle, Elton John, Andy Murray, Peter Kay, Suranne Jones and David Tennant, not to mention a selection of ordinary people – all enthusing about what Connolly has meant to them.

Some of his watching fans, however, read too much into the programme and thought it was an obituary. “Did I miss something … has Billy Connolly died?” asked one on Twitter. Another put the question: “Why is @ITV showing an obituary for Billy Connolly? Please tell me he’s okay”.

Connolly may be coming up for his 75th birthday, and coping with serious illnesses but, true to form, he has no intention of bowing out quietly. Contrary to fears that have been expressed in some quarters a source close to Connolly comments, “He is definitely not planning on fading away – guaranteed. He was out and about filming with the BBC this week in Glasgow.”

Connolly said in an interview that last month that he “lives in hope” of performing on stage again, adding that he would “have to see how this medicine works out”, referring to a course of Parkinson’s medication he had embarked on.

Three years ago Connolly disclosed that he had been diagnosed with prostate cancer and Parkinson’s Disease on the same day. His health issues, then, might determine otherwise but it seems he really has no intention of calling it a day.

Connolly, who now lives in Florida with his wife, Pamela Stephenson, the psychologist and author, can be seen this Wednesday in an entertaining BBC One Scotland documentary, Billy Connolly: Portrait of a Lifetime, in which he admires three outsize murals of him, painted by top Scottish artists John Byrne, Jack Vettriano and Rachel Maclean.

The murals, commissioned by BBC Scotland in conjunction with Glasgow City Council’s City Centre Mural trail and Art Pistol Projects, have been translated into stunning and dramatic wall-ends in Dixon Street, Osbourne Street and the Gallowgate.

Connolly has clearly been blown away by them. “I’m truly amazed at the effect these have had on me”, he says in the programme. “They’ve just completely stunned me. I thought I’d be all light-hearted on seeing them and jokey – but they’re so big – the effect on me is so profound…..You know… people going to that length for me….. it’s just taken my breath away.

“I’m just flabbergasted… overjoyed… it’s been a brilliant experience – being painted and otherwise by these genius people taking the time to do it….. it just takes my breath away… I love it…”

Byrne describes his old friend as a “phenomenon … he is a one-off. He is larger than life”. Indeed he is. Connolly has been making us laugh since the 1970s with his anarchic take on life, his creative use of swearing, his willingness to confront every subject under the sun.

An indelible memory for millions of TV viewers of a certain age is his debut on Michael Parkinson’s chat show in 1975, the enduring highlight of which was the joke that ended with the punchline, "I need somewhere to park my bike". Comedian Jack Dee, who watched the show as a teenager, would later speak about the impact that the joke had on him. Overnight Connolly, the former shipyard welder-turned-folkie, became a comedy superstar.

Every diehard Connolly fan will have his or her favourite routines: the incontinence-trousers sketch, for instance, which had a celebrity TV audience, including Clive James, in hysterics; the two Scotsmen in Rome; the colonoscopy routine; the Crucifixion, one of his very earliest set-pieces. There have been killer one-liners galore.

He is fearless when it comes to scatological humour, fearless when it comes even to finding humour in such things as the Glasgow Airport terror attack – “What were they f---ing thinking about – bringing terror to Glasgow? Bad choice, boys!”

In a 2012 poll he was voted the UK’s most influential comedian of all time. The organisers, TV channel Dave, said Connolly and his friend Robin Williams, who was voted top international comedian, had both “consistently pushed the comedy envelope … they are still the funniest men on the planet”.

Michael Parkinson, presenting him with an award last year, listed his multiple achievements – singer, musician, actor, film star, explorer, adventurer and philosopher. “He is also the stand-up comedian by whom all others are judged.”

Over the years Connolly has done substantial amounts of TV and appeared in films as diverse as The Big Man, Mrs Brown (in which he did an excellent job as Queen Victoria’s rugged Highland servant and was nominated for two Bafta awards), The Debt Collector, The Last Samurai, Quartet, Brave (in which he voiced King Fergus) and What We Did on Our Holiday. He has received honorary doctorates and awards – a CBE, for services to the entertainment industry, was announced in June 2003.

The force of nature that is Billy Connolly may have been subdued somewhat by his illnesses, but he remains widely venerated, by fans and celebrities alike. On his official Facebook fan page there are heartfelt testimonies from people who saw him on his High Horse tour late last year.

“Saw my man Billy Connolly this evening” one reads. “After everything he has been through, is going through and is yet to go through, he still laughs and enjoys making others laugh, smile and forget their own problems for a while. That takes a truly special person, one of a kind”.

• Billy Connolly: Portrait of a Lifetime, BBC One Scotland, 9pm, Wednesday.