The Walmington-on-Sea Home Guard platoon has seldom looked shabbier. And not in a good, comic way. It’s 1944 and as the Allied forces are gearing up for a last push, MI5 agents have traced a rogue radio transmission emanating from the coastal English town populated by Captain Mainwaring’s makeshift platoon. Might a newly arrived and impossibly glamorous journalist (Catherine Zeta Jones) be messaging Berlin?

Sadly, the men are too dazzled by her Chanel suits and charms to notice. And so the German spy is alternately courted by Mainwaring (Toby Jones), his Oxbridge nemesis Sergeant Wilson (Bill Nighy), resident spiv Walker (Daniel Mays) and the guileless Pike (Blake Harrison).

When the new Dad's Army sticks to old jokes, it serves some purpose. To this end, there are lovely, silly supporting turns from Tom Courtenay as the flappable Corporal Jones, Michael Gambon as ancient Godfrey and Bill Paterson as Private Frazer.

But too often we’re stuck in tea shops on dates with Mrs Douglas. The film’s attempt to accord more screen time to the wives who were seldom – and in Mrs Mainwaring’s case, never – glimpsed in the original series, is commendable, but it does rather muddy the original alchemy.

That goes double for the Mainwearing-Wilson rivalry: Toby Jones channels Arthur Lowe's inverted snobbery with aplomb, while Bill Nighy channels Bill Nighy, thereby rendering the film's many class jokes entirely impotent.

Even with Jones barking the beloved catchphrase "you stupid boy", fans of the TV show will likely be disappointed and newcomers will likely be baffled. Dad's Army was an improbable hit 40 years ago. Now, even the farcical moments look farcical.

Who do you think you are kidding, fake Dad's Army?