Tony Slattery: A shining star of the 1980s alternative comedy scene

But behind the scenes he struggled with bipolar disorder. Five years ago he revealed he had gone bankrupt following battles with substance abuse and mental health issues.

He said “fiscal illiteracy and general innumeracy” as well as his “misplaced trust in people” had also contributed to his money problems.

In a BBC Horizon documentary, What’s The Matter With Tony Slattery? he said he had been sexually abused by a priest at the age of eight but had never told his parents. He believed the experience contributed to his unstable character later in life.

Tony Declan James Slattery was born in Stonebridge, north London, the fifth and youngest child of Catholic Irish immigrants, Michael and Margaret Slattery.

He attended Gunnersbury Boys’ Grammar, where he won a black belt in judo and was picked for the England under-15 team, before winning a scholarship to Trinity Hall, Cambridge, where he read modern and medieval languages.

It was at Cambridge that he discovered his love of the theatre, taking delight in making audiences laugh. He met Stephen Fry, who invited him to join the Footlights and he found himself in the company of Sandi Toksvig, Jan Ravens and Richard Vranch, as well as Thompson and Laurie.

He broke into television as a regular performer on ITV’s Saturday Stayback, Chris Tarrant’s 1983 follow-up to the ‘adult Tiswas’ known as O.T.T. He was also in Yorkshire TV’s children’s drama Behind the Bike Sheds and the Saturday-morning show TX.

In 1988 he was in the first series of the comedy improvisation show Whose Line Is It Anyway? With Clive Anderson and quickly established himself as a regular. On the strength of it, he and co-star Mike McShane were given an improv series of their own called S&M.

As a dramatic actor he appeared in The Crying Game, To Die For and Peter’s Friends, directed by Kenneth Branagh and co-starring Fry, Laurie and Thompson.

At the end of the 1980s Slattery became a film critic, presenting his own show, Saturday Night at the Movies. He also appeared in the ITV sitcom That’s Love with the actor-producer Jimmy Mulville, another graduate of the Footlights.

Off-screen, Slattery was a regular guest with the improvisational Comedy Store Players and had prominent roles in the legitimate theatre, receiving a 1995 Olivier Award nomination for best comedy performance for the Tim Firth play Neville’s Island, which was later made into a film starring Timothy Spall, and starring in the wartime comedy Privates On Parade, based on the film of the same name.

His West End debut was in the 1930s-style musical Radio Times, and on TV he also played a detective in Tiger Bastable, a gentlemen comedy spoof, and the title character in sitcom Just A Gigolo.

But as his personal problems took over he retreated further into himself. “I rented a huge warehouse by the River Thames,” he said. “I just stayed in there on my own, didn’t open the mail or answer the phone for months and months and months. I was just in a pool of despair and mania.”

In recent times he had toured in a comedy show and launched a podcast, Tony Slattery’s Rambling Club.

He is survived by his partner of three decades, the actor Mark Michael Hutchinson.