Pity John Sessions? Heaven forbid! This, after all, is a man who describes himself as being a "bit punchable". Then there's that Spitting Image puppet: "They did John Sessions going up his own arse," he recalls of the Eighties satire, somewhat proudly. "And I remember Roger Mellie, the man on the telly in Viz, beat me up in one cartoon," he adds, warming to his theme.
Yet it is compassion that he'll need on Thursday night when he plays his first role in nearly two decades at the Hampstead Theatre. The actor-cum-comic-cum-general-smart-alec will be desperately hoping to avoid a repeat of the stage fright that spelled curtains for his life on the boards all those years ago.
"I was doing a big run in the West End and one day I got very frightened. Or more precisely, I persuaded myself that I was frightened of getting on stage. It was like falling off a bike. I should have got on the bike again straight away and done as much theatre as possible immediately thereafter, but I didn't." Which explains why, for me at least, he's remained somewhat frozen in time as that man off Whose Line Is It Anyway?
Sessions has his old friend William Boyd to thank for reviving his acting career, assuming all goes well. It was Boyd who asked him to take a part in Longing, the novelist's first stab at a play, which is based on two Chekhov short stories: A Visit to Friends and My Life. The pair go way back, to a dinner at Ian Hislop's house, where Sessions "spent the evening being Anthony Burgess and Dirk Bogarde". As you do. Or you do if you're Sessions, who is a mean mimic along with everything else.
The actor is tapping into his Scottish roots – he was born in Largs 60 years ago, but left Scotland for Bedford when he was three – for his role in Longing, which he is playing as a Glaswegian. "You've finished reading the play? Oh, well done," he says, when we meet during a lunch break last week, just before the cast's second run-through. No doubt meant kindly, this is one of just many Sessionsisms that leave me feeling peculiarly patronised by the time we're done.
It was, for the record, an easy read as befits something by Boyd. More importantly, I'm hungry to see the play when it opens. I'm no Chekhov expert, but it covers all of the Russian master's main themes – from disillusionment and identity to cultural futility and unrequited love. Possibly a bit too well, although Sessions insists enough of Boyd comes across to rescue it from any charge of stereotype. "It's Boydov," he says. "It's Chekhovian, but it's got an extra voice to it, which is Will's voice. Even though we're set in 1892, people might find there's something fresh and contemporary about the relationships." He admits "some people can be very proprietorial about their Chekhov", but doesn't think Boyd takes "any great liberties".
One way and another, it will be an emotional week for Sessions, who is mourning the loss of his friend Richard Briers. Rehearsal schedule permitting, he will be at this week's funeral. "I got the news on Monday night when I got home and turned on the computer. 'Richard Briers is dead.' It was a horrible way to find out." It was, "funnily enough", Sessions whom "Dickie" had to thank for his stage career taking off. Sessions was the link between Briers and Kenneth Branagh, who came to watch a play the pair were both in. "Ken came down to Chichester to see me [the two are chums from Rada days] and saw Dickie. Within a year or so, Dickie was playing Malvolio in Ken's Twelfth Night, and then he was in Much Ado. He was Bardolph in Henry V, and Polonius in Hamlet. So he did an awful lot with Ken."
Briers being Briers, the funeral will involve much reminiscing between old luvvie pals and many "unrepeatable" stories. I press Sessions for some, but am denied anything juicy. "Dickie dropped a dreadful clanger with Denzel Washington once, but I can't tell you what it was. No, I can't tell you." Grey-haired head in hand, he racks his brains: "There was one story, him and Robert De Niro, that's quite a combination. When they did Frankenstein they were having a little chat about where they both lived. Dickie was trying to describe Chiswick to Robert De Niro. And Robert De Niro wasn't really getting it. Dickie did say at one point, 'It's no point having all his money when he's as mad as he is. I wouldn't want to be that rich, and that mad.' "
He says all this without giving me a single syllable of De Niro's New York twang, which leaves me feeling cheated. I am similarly swindled out of any good anecdotes about the times he's come a cropper with an impersonation too far. The ones I get – about annoying Harold Pinter and avoiding annoying Al Pacino – are decent enough but merely repeat stories I've already heard. (Pinter took it "extremely" badly when Sessions referred to his wife, Antonia Fraser, as Lady Antoinette Fridge Fraser in a skit. "Harold took this to mean I was implying she was frigid." And while on set with Al Pacino, "Al liked me doing various people, but there was no question of doing him. I think there would have been a very sudden sense-of-humour failure.")
I do get Sessions in a tiz, however, after asking the "plastic Scot" his views on Scottish independence. "It's absolutely ridiculous. I think it's a waste of money. Och, it's just nonsense. Have one parliament, Westminster. Get rid of the European bloody Parliament, the Scottish assemby, or Parliament, I should say, the Welsh Assembly. They're just money spinning … oh God, they make me so angry."
He's adamantly "anti" Europe. "I get so bored with people going, 'Ukip are a bunch of racists.' They're nothing of the kind. Nigel Farage talks more sense than the rest of the politicians put together. The United States of Europe is madness. This whole business with Germany and Greece. These people, Susie, get paid to think about these things, all day long. And I can't believe they went, 'Well, here we are, we've got these people in Germany, and they get up at six in the morning, and they work until eight in the evening, and these people in Greece fall out of bed at 11, go and play backgammon, drink a bit of coffee, go and have a siesta and then do an hour's work.' And they expect to get the same benefits, welfare rights, and all the rest of it."
A Ukip luvvie – who'd have thought it? Sessions being Sessions, there's no point arguing. He's just too sure that he's right. I'm not quite at the "punchable" point, but perhaps Sessions hits the nail on the head with a comparison between himself and Stephen Fry, that other mega know-it-all. "Stephen manages to be so much more demotic. He wears his knowledge very lightly. I tend to sound a bit more like, well, a creep really. It's my imparting of the information with a certain little bristle of pride or something."
Perhaps he won't be needing that pity after all.
1953 Born John Gibb Marshall, on 11 January, in Largs, Ayrshire. Has a twin sister, Maggie, and an older brother. Grows up in Bedfordshire after his father, a gas engineer, moves the family when he is three years old.
1964 Attends Verulam School, in St Albans. Later gets an MA in English literature from Bangor Univeristy. Spends four years working on a PhD from McMaster University, in Canada but doesn't complete it.
1979 Turns instead to acting after getting into Rada, where he meets his great friend Kenneth Branagh.
1982 Gets his first film part in The Sender. Works the comedy circuit, including topping a double bill with French and Saunders. Within a few years he is impersonating politicians on Spitting Image, where he earns the dubious distinction of being the only mimic to get his own puppet: he is Branagh and Emma Thompson's pet cat. Makes his name doing improvisations on Whose Line Is It Anyway?
1995 Appears in My Night with Reg, at the Royal Court, where he suffers a bout of stage fright and abandons theatre acting.
2002 Is in Gangs of New York. Becomes a regular panellist on shows such as Have I Got News For You, and, later, QI.
2010 Plays Harold Wilson in Made in Dagenham. He is Edward Heath in The Iron Lady a year later.
2013 Returns to the stage in William Boyd's Longing at the Hampstead Theatre.