Simon Cartwight as Frankie Howerd and Mark Farrelly as Dennis Heymer in Howerd’s End [Steve Ullathorne]

UNLIKE Heinz soups, comedians tend to come in just two varieties: those for whom performing is in their DNA – they’re never “off”. Think Mel Brooks or Eric Morecambe. Then there are those who really have to work for their laughs, off-stage they’re often serious, even morose.

Step forward Francis Alick Howard, aka Frankie Howerd.

Here was a man who was basically a thwarted straight actor. A born worrier, he really did fret his hour upon the stage. Every tic, every gesture, every “ooooh” and “aaah” was rehearsed to the nth degree. His act, born of nerves, was not the usual stand-up routine – he would stretch one joke to breaking point, the rest was a sea of anfractuous scuttlebuttery, conspiratorial asides, facial contortions and mock outrage, topped off with a healthy dollop of non-sequiturs.

His pioneering style may have made him a comic maverick but it also made for a turbulent career. Prone to the vagaries of fashion, his comebacks were legion.

A huge radio star in the 50s, his star waned in the 60s. On the verge of turning it all in and opening a pub, he became the unlikely darling of the satirical set after appearing on That Was the Week That Was and at Peter Cook’s Establishment Club. A decade later, his toga-fest, Up Pompeii!, saw him turn into TV’s king of innuendo, and finally, just before his death in 1992, he was discovered by younger fans appreciative of his take on “alternative” comedy.

Despite his success, however, Howerd was never content. A gay man in an age when his sexuality would have been professional suicide – and indeed illegal – he was never happy in his own skin. His lifelong partner Dennis Heymer was a constant presence, but one that was kept under wraps, frequently palmed off as his “manager” or “chauffeur”.

And it’s that relationship that’s at the heart of a two-hander, Howerd’s End, written by Mark Farrelly, who appears as Heymer, and Simon Cartwright, who plays, or rather inhabits, Howerd.

“He was ahead of his time,” says Simon. “He was the Picasso of comedy.”

By that he means Howerd broke all the rules; he was not slick or smooth, he was a highly controlled shambles.

“He really was one of the last links to the front-cloth patter comedians – but he took it off in a direction that was unique,” observes Simon.

Simon sans Howerd’s toupée

“I’ve analysed his act and the first 20 minutes was often an apology. He’s saying to the audience ‘now look, I feel sorry for you. I know what’s coming and I know it’s rubbish but I’m begging you to force yourselves to laugh cos it’s tough up here’. It’s a very clever device and something he honed over 50-odd years.”

The play is, Simon stresses, just that: a play, not a tribute show. He has approached the part as he would any other but as it’s subject is a well-known one, is aware there is an element of impersonation.

And as a former impressionist – he once had an act with Alistair McGowan and has performed as Bob Monkhouse on a number of projects – Simon knows exactly what’s required.

“I’m a musician. I started out as a guitarist so I’ve got a head for notes, which I think really helps. I’ve always found voices are like music, they have a natural tonic, a home note, the middle C. Every voice has a middle C and it’s really down to luck whether your voice has a natural compatibility with the voice you’re trying to imitate.”

He also watched impressionists doing impressions of Howerd. “I studied what they did and made sure I never did that – that’s the way to kick out clichés.”

Accepting the part, however, presented one problem: although he admired Howerd, he didn’t like him.

“I met him 39 years ago at the Churchill Theatre in Bromley as an 18-year-old. I got an autograph but I also got a fairly unpleasant experience, he was very sharp and unfriendly – it kind of shattered the illusion of who this great man was.”

When he took on the role he thought he’d have to learn to like him, something he’s grown to do. And to say Howerd was a complicated man is an understatement.

Following his death, for example, countless accounts of Howerd’s promiscuity came to light. And as someone with first-hand experience of Frankie hanky-panky, I can vouch for their veracity.

Early on in what I am pleased to refer to as my career, to my (and his agent’s) surprise, Howerd agreed to an interview.

At his office in Kensington, he suggested we talked in the attic. Surrounded by old props and memorabilia, he grudgingly answered my questions, never for one moment making eye contact. As time passed he grew increasingly irritable, leaving me with the distinct impression he did not like me.

It was therefore an even greater surprise when, taking down his trousers, he produced a pot of ointment and enquired whether I’d be prepared to rub it into his upper thigh.

Fortunately, experience had alerted his agent to my predicament. She loudly announced her presence on the stairs and the trousers were hastily returned to their customary position.

My sympathy, therefore, has always been with Heymer, and the play, says Simon, gives Dennis a voice, an opportunity to give his side of the story. Both therapeutic and cathartic, it’s essentially about regret.

“You can apply the principles of this story to any relationship. It’s not just a gay relationship, it’s about partners who take each other for granted for years and years and then there’s that moment when you can’t be together and you wish you’d said ‘I love you’ and you never did.”

• Howerd’s End is at The Museum of Comedy, The Undercroft, St George’s Church, WC1A 2SR on April 16 and 23, and The Crazy Coqs, Brasserie Zedel, 20 Sherwood Street, W1F 7ED on September 3.