It was neither. The winner, another mimic called Tony Maiden, would go on to commit suicide. Does he still think about him? “Yes very much. He died tragically young. I’m very lucky. I’ve watched a lot of people that I was alongside fall at the fences.” In 1984 he and Dustin Gee were performing on LWT’s Live at Her Majesty’s while Tommy Cooper, who had just had a heart attack live on TV, was dying behind the front cloth. Did he feel the symbolism of the moment as an older school of entertainment died too? “We were conscious of that afterwards. The audience didn’t know what had happened. Jimmy Tarbuck says, ‘Are you guys ready to go on?’ We were thrown on. In some kind of weird way it was the night that we became noticed by the public.”

In recent years the wheel has come full circle as, stouter and a little less blond, Dennis has twice been cast as washed-up comics from yesteryear. In Jigsy, which is on the Liverpool Everyman’s YouTube channel, he sorrowfully recalled the good old days. In End of the Pier at the Park Theatre in north London he played a has-been called Barry Cheese.

Halfway through our hour together, someone brings in Sir Joseph’s wig, a strawberry blond bouffant creation that looks uncannily similar to Dennis’s actual hair in the 1970s. I’m reminded of Bob Monkhouse’s prediction. “Les,” he once told him, “you might lose the hair, you’re not the funniest comic but you have charm and that will always see you right.” Was he right? “He did sum up what he thought my career would be. I’m still here…”

HMS Pinafore is at the London Coliseum, WC2, from tomorrow. Tickets: ENO.org

The best of Gilbert and Sullivan, by Mark Monahan  

Pirates of Penzance (1879) 
All frustrated buccaneers and comely maidens, this 1879 confection is also – it is safe to say – the only opera (G&S or otherwise) to use a leap year as a plot device, or indeed have a chorus of: “With many cheerful facts about the square of the hypotenuse.” The latter comes from the blistering, deservedly famous Major General’s “patter” song, but there are plenty of other entirely unforgettable tunes, and Pirates (which launched in New York) is the very definition of ridiculous good fun.

The Mikado (1885) 
G&S’s ninth collaboration was a resounding success on its premiere at the Savoy Theatre, where it ran for 672 performances. In recent years, this perky love story’s Japanese setting has drawn ire, chiefly in the US, but the piece’s (fictionalised) Far Eastern milieu was, in fact, created as a means of slyly holding British, not Japanese, politics and society up for ridicule. At any rate, the superabundance of once heard, never forgotten melodies – from I’ve Got a Little List to Three Little Maids From School Are We – still keeps audiences coming back in droves, with Jonathan Miller’s 1987 production for ENO the definitive staging of the modern era.