It is a sound that cannot be unheard. It is just one word that has immortalised John Challis in the British consciousness. “Marleeeeeeeeeene,“ he whines down the phone to me in the nasal tone of his Only Fools and Horses character Boycie, transporting me instantly to the world of Del Boy, Rodney, the Nags Head and endless wheeling and dealing.

“It was a stroke of luck really,“ he says, switching back to his clipped received pronounciaiton to talk about how he landed a part in the BBC show, which went on to pull in viewers of 24.3 million and was voted Britain’s Best Sitcom in 2004.

Brought up in Epsom, he dabbled with being an estate agent before following his heart onto the stage and landed roles at the National Theatre and the Royal Shakespeare Company alongside renowned actors such as Sir Ian Holm.

But it was his innate talent for mimicking those around him that decided his fate after John Sullivan cast him as a policeman in his first television series Citizen Smith, starring Robert Lindsay.

“I played so many policemen so I went along thinking ’what can I do that is different?’ and invented this policeman with all of the characteristics of someone I used to know in a pub back in the ’70s, including their sort of pedantic way of talking and superior attitude – it was that copying people which I have done since I was a kid.

“John came and said: ’I really like what you did with that character, I’m going to try and use it again one day’ and I thought nothing of it really.“

A year later the writer made good on his word by asking John to play a secondhand car salesman in his next project, a sitcom set in Peckham about a family called the Trotters.

“Nobody said there would be another series, and certainly nobody said the character would come back again,“ says John. “So it was a complete surprise when it came back the following year, by which time I was at the National Theatre,“ he laughs.

“I have had this double life really with situation comedy and trying to be a serious actor,“ say John who will be in St Albans this month to reveal secrets from the set of Only Fools and Horses and tell stories and anecdotes from his career.

So who was the real man who he met in St Margaret’s Hotel opposite Twickenham Film Studios and based Boycie on?

“All I remember was his name was Gordon and I think his second name was Mackintosh and he was a bit of a man of mystery and a bit of a loner and an odd, slightly sad character. But he really thought he was something special and he absolutely fascinated me, so I pinched a few of his characteristics and used them later.

“So it’s lucky I met him I suppose.“