Towards the end of Eric and Little Ern, I realised that I was suppressing a fairly urgent desire to climb onstage, grab Jonty Stephens’s jowly face and shout at him, ‘Are you a real person? Are you? ARE YOU?’, and then to seize Ian Ashpitel by the lapels and demand, ‘Is this a double act? What is it? WHO ARE YOU, LITTLE ERN, WHO ARE YOU?’ It was evening of turbulent emotion.

Because this is a strange show, really, when you think about it. Two men impersonate Morecambe and Wise and everybody laughs, because Morecambe and Wise were quite funny. Not brilliantly funny, not genius, but they had some good, solid gags. And almost everyone in the audience knows and loves these gags, or they wouldn’t have to come to see the show. So when they clap, are they clapping Morecambe and Wise, or Stephens and Ashpitel? Half the time the audience laugh before the joke’s even been done. When Stephens walks over to a window and a siren whoops and fades outside, everyone laughs. When Ashpitel starts singing and Stephens takes a brown paper bag out of his jacket pocket, everyone laughs. When Stephens opens the mouth of a plastic skull, half the front row shouts “Rubbish!” I mean, any lanky man with male pattern baldness could have found a pair of thick-rimmed glasses and a short mate with wonky grey hair and got a good few chuckles onstage that night without even needing to look at a script.

But Stephens and Ashpitel are talented in their own right, I think. It’s hard to tell, but they’re certainly good at doing impressions of Morecambe and Wise. An admittedly fairly niche discipline, but they’re definitely acting, at least, and doing it well. Stephens’s Morecambe is particularly well-observed, with all the right facial tics and a lovely Lancastrian burr. He’s also got the physical comedy, the kind of grace-masquerading-as-clumsiness that Eric Morecambe was an absolute master of, and without which the impression would fall flat on its face. There’s a nice moment with the skull where he messes up the ventriloquist act – it’s not in the original show, but he improvises a joke in a very Morecambe-esque way, and it works all by itself. As Ernie Wise, the straight man, Ashpitel has the hard job, but he does a good rueful acknowledgement of awful puns. He’s a bit stouter than Wise, but that doesn’t harm his fussy, self-righteous bustling.

The story’s a bit weak – Ernie is dying in hospital, and his old partner Eric, 15-years-dead, comes back to reminisce about old times. That’s the first half. Then they abandon plot completely post-interval, and the second half is simply pure Morecambe and Wise front-of-curtain banter. It’s largely a ‘Best Of’ of Eric and Ernie back-and-forths, with a few lines of original material. Much of the play’s credit should probably go to Eddie Braben, the double act’s main writer from 1969.

So it’s not clever, Eric and Little Ern, it doesn’t think about itself in the way that The Play What I Wrote did. It’s affectionate, and it inspires affection through shamelessly manipulating the audience’s nostalgia. Everyone knows that’s what it’s doing, and they’re happy to go along with it. It’s a Christmassy show, a gentle celebration of two funny men. I think most of audience managed to avoid a crisis of existential doubt, and left the room with only ‘Bring Me Sunshine’ going round in their heads.

Eric and Little Ern plays the St James Theatre until 11 January 2015. For more information and tickets, see the St James Theatre website.