Unless you’ve just returned from a year on a remote Pacific atoll – and if you have, I’m not atoll jealous – you’ll know that a film, based on a 40-year-old television sitcom, is currently on release in cinemas.

“Love Thy Neighbour – The Movie” stars Samuel L. Jackson and Jim Davidson.

Just kidding!

It’s “Dad’s Army”, which boasts a stellar cast, including Swansea’s Catherine Zeta-Jones as Captain Mainwaring.

Just kidding again! She plays a suspected German spy.

Since I first heard it was in production I’ve been puzzled why its producers thought a film based on a TV sitcom set in the 1940s, that was first broadcast (in black and white!) in 1968 and ended in 1977, would be a potentially commercial venture.

Now you may say “Ah, but these film people know what they’re doing”, to which I would refer you to the words of esteemed screenwriter William Goldman

“Not one person in the entire motion picture field knows for a certainty what’s going to work. Every time out it’s a guess and, if you’re lucky, an educated one.”

I hope the “Dad’s Army” film does well, but wonder if fans of the TV series will venture out cold winters nights  to see an expanded version of a TV show that still gets respectable viewing figures for its Saturday night repeats on BBC 2 – which seem to have been running since the original series ended!

Film versions of TV sitcoms were very popular in the 1970s – indeed a “Dad’s Army” film was made in 1971 featuring the original cast and was a modest success.

Just before “Star Wars”, “Indiana Jones” and their sequels turned our studios around, these big screen ‘spin-offs’, made quickly and cheaply, kept an ailing British film industry busy.

However, most of them were terrible and are almost impossible to sit through today.

There were exceptions like “Porridge”, but there was much dross, like the three (yes…three!) “On The Buses” films and “Are You Being Served?” in which the staff of Grace Brothers all went on holiday to a Spain that strangely resembled a corner of Pinewood Studios.

If the new “Dad’s Army” film makes tons of money, could it start a new raft of big screen ‘spin offs’, such as “Citizen Khan” or “Benidorm”?

No, relax. It’s about as likely as, say, the BBC hiring Hollywood star Matt Le Blanc from “Friends” to co-host “Top Gear”.

Ooops!