IT never bothered comedian Mark Steel that he had never met his mother.

"It didn't occur to me I needed to meet her to 'find out who I was' as it didn't seem likely I'd discover I was someone different to who I thought I was," says Mark, who was adopted. "Could it turn out that I was three stone lighter than I thought, or I spoke Italian or supported Arsenal or had a fear of Liquorice Allsorts?

"But after the birth of my own son, I realised it's quite an event to have a child, and she may well remember giving birth to me, and maybe even the adoption."

So began a 12-year odyssey of discovery. and now he tells his story of surprises in Who Do I Think I Am?, on tour at Harrogate Theatre on April 1 and Leeds City Varieties on April 15, as he switches from the geographical journeys of his BBC Radio 4 series, Mark Steel's In Town, to a personal one.

Steel charts how his life started in an ordinary family in an ordinary house in Swanley, in north Kent, but his research led him to the glamour of the Swinging Sixties in London, the British royal family and even Lord Lucan.

Mark was adopted by Ernie and Doreen in 1960 when only a few days old and was their only child. It was a close family; he always knew he was adopted and was not interested in finding his birth parents until he became a father himself. Whereupon he started to trace his birth mother; “I thought she might remember me,” Mark says drily.

"So over a 12-year period I tracked her down. She didn’t want to meet me, she told the researcher who contacted her, but she did say who my father was."

It was then that the astonishing details of his birth parents, Frances and Joe, who were both barely in their twenties when he was born, started to emerge.

"To start with, and this was only a gentle opener compared with what was to come, Joe was the world backgammon champion of 1976. He was a multi- millionaire trader on Wall Street, had been the closest friend to Kerry Packer, and an associate of the royal family," reveals Mark.

Joe, who now lives in the United States, used to gamble at the famous Clermont club in London alongside “Lucky” Lucan, who disappeared in 1974 after his children's nanny was murdered. Members of the royal family, meanwhile, were regular visitors to Joe's home when his family lived in London.

"This didn’t seem entirely at ease with all my years as a socialist," says the old-fashioned leftie comedian with a Marxist slant, whose column for the Independent regularly skewers politicians of all shades.

"When I met Joe he told me he’d paid my natural mother to have me ‘dealt with’. I told him I was now in touch with her family, so I could try and get him his money back if he liked."

Mark is still uncovering his remarkable tale. “Every time I do a bit more research, it just keeps getting more absurd, like a badly written novel by Jeffrey Archer,” he says, laughing at the thought. “People would be entitled to say, 'Come on mate, you're just making this up', because it seems so far-fetched. But I promise you, every word is true; I haven't even slightly exaggerated a detail for comic effect.”

Premiered at the 2015 Edinburgh Fringe, Mark's show is amusing but tear-jerking too. "People say, 'Oh you're so brave',” he says. “And I reply, 'No, it's not brave. Doing it in Raqqa would be brave'.”

He has no truck with false sentiment. “The resolution of the story is that it's all turned out OK; it doesn't have to be a big emotional song and dance,” he says.

Mark admits, however, that his views on the nature-versus-nurture debate have changed. “Before I started this process, I would have been adamant that you are just who you are, but now I think it's a bit of both," he says.

"Clearly I can't now argue that case. I think we are an unfathomable mixture of environment and something that's in our genes, and to come down hardline in either direction is equally daft. It's a complicated mix that you cannot predict.”

Mark has two children and so can muse on nature versus nurture in his own home. His son, Elliot, 19, is a stand-up comic himself, while his daughter Eloise, 15, shows talent as a comic actress. While proud of their achievements, he bats off any suggestion they have inherited their talent from him.

“With my son, whether it's something genetic which means his brain is hard-wired in a particular way, or whether it's because he's been around comics all his life and can easily imagine a career in the industry, who knows? For many people comedy would be an impossible dream, but for him it was a perfectly normal career option," he says.

"My daughter's a very good actress; she was in a musical at school recently and she was brilliant and I genuinely mean that. But I'm not going to push her in any direction.”

When Mark is doing his radio show, he usually takes at least a day to walk around town, going into libraries, cafes and museums to chat to folk to uncover the area's interesting stories and quirky locals, but he has less free time on this tour.

Nevertheless, he may bump into someone who knew his birth father, as happened during last summer's Edinburgh run, when a solicitor approached him after the show and said: “I once met Joe.”

Mark Steel, Who Do I Think I Am?, Harrogate Theatre, April 1, 8pm; Leeds City Varieties, April 15, 8pm. Box office: Harrogate, 01423 502116 or  harrogatetheatre.co.uk; Leeds, 0113 243 0808 or cityvarieties.co.uk

By Veronica Lee and Charles Hutchinson