Like all right thinking people, you hated the idea of a film version of the nation’s most beloved sitcom.

But when you heard the cast they had assembled perhaps you thought well, maybe.

After seeing the results I am still not convinced it was worth doing but once, or if, you accept that these characters can be played by other people, then this gets more things right than wrong.

Finding full-length plots for sitcom movie versions has always been tricky.

Set in 1944, this one has the home guard in Walmington-on-Sea charged with finding a Nazi agent who is Zeta-Jones posing as reporter from The Lady magazine, there to do a piece on them and getting Mainwaring (Toby Jones), Wilson (Bill Nighy) and Pike (Blake Harrison from The InBetweeners) all riled up.

It isn’t a great plot, (it’s inappropriately big – the success of D-Day depends on it and there is even a battle scene) but it does the job.

Some of the casting is spot on, which is a relief as this comes from the team that thought that Russell Brand might adequately replace George Cole as Flash Harry in their St Trinian’s films.

Jones and Nighy are an obvious fit as Mainwaring and Wilson, but the film’s great triumph is Michael Gambon as the frail, doddering Godfrey.

His is the performance that is closest to an impersonation of his TV equivalent, and it’s the funniest and most charming.

And that’s important because I think the genteel and impeccably polite Godfrey and two sisters are the key to the series – they are what we were fighting for.

In the first film version, with the TV cast, there is a moment when Arthur Lowe gets to stand on some white cliff and proclaim that we are going to win this war.

It’s enormously touching because it says something rather great about us as a nation that these well-intentioned buffers are our most resonant fictional representation of the great fight against fascism; but also because Mainwaring – pompous deluded little Mainwaring – is going to experience something Hancock, Steptoe, Fawlty and Brent never did: he’s going to win.

Seventy years on and it is still a victory worth celebrating.