COMEDIAN Mark Steel was not really bothered that he had never met his mum.

"It never occurred 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 the left-wing stand-up, broadcaster, newspaper columnist and author. "Could it turn out 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 [Elliot, now 19], 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."

This prompted Steel to look into his back story, leading to his latest touring show, Who Do I Think I Am?: more of an emotional journey this time after the geographical travels for his regular BBC Radio 4 series Mark Steel's In Town.

As his York Theatre Royal audience will learn on October 19, Steel's show charts a story of discovery that began in an ordinary family in an ordinary house in Swanley, in north Kent, and leads to the glamour of the Swinging Sixties in London, the British royal family and even Lord Lucan.

Steel had been adopted by Ernie and Doreen in 1960 when only a few days old and was to be their only child. The family was a close one; he always knew he was adopted and was not interested in finding his birth parents. Until that moment when he became a father himself: the spark that ignited his search to trace his birth mother. “I thought she might remember me,” he says.

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.

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

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Mark Steel: "Then it gets more interesting"

"To start with, and this was only a gentle opener compared with what was to come, he 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.

"This didn’t seem entirely at ease with all my years as a socialist. When I met him, 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. That’s the first part of this story. Then it gets more interesting…".

Steel, 56, is not only the offspring of a wealthy former Wall Street trader, but also has a direct connection to several other international capitalists and playboys. Joe, who now lives in the United States, used to gamble at the 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.

Steel premiered the show at the 2015 Edinburgh Fringe but is still uncovering more revelations. "Every time I do a bit more research, it just keeps getting more absurd, like a badly written novel by Jeffrey Archer,” he says. “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.”

Amid the humour in Steel's storytelling, there are moments of sadness too, but he says: "People say, 'Oh you're so brave', and I reply, 'No, it's not brave. Doing it in Raqqa would be brave'.” False sentiment has no place in his tale: "The resolution of the story is that it's all turned out OK," he says. "It doesn't have to be a big emotional song and dance.”

One change has emerged from Steel's search, however: his views on the nature-versus-nurture debate. “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 Steel: Who Do I Think I Am? York Theatre Royal, October 19, 8pm. Box office: 01904 623568 or at yorktheatreroyal.co.uk