How do you stop any form of entertainment becoming out of date? In these technologically advanced days anything can become passé almost as soon as it's written. So writers often resort to setting their opus in the past, with astonishing results. Probably the best example of this on television is Dad's Army.
In the theatre any prize for longevity must surely go to The Mousetrap which is still pulling in the crowds, albeit in a small theatre, more than half a century after it was first performed. As far as musicals are concerned, there's nothing to touch The Boy Friend.
It's difficult to believe that a song-and-dance show about a finishing school on the French Riviera in the Roaring Twenties is celebrating its 50th anniversary and is touring the country again. But The Boy Friend succeeds despite its old-fashioned façade, its outmoded innocence and its contrived storyline.
It's the perennial saga of boy meets girl, boy loses girl through a misunderstanding before the truth is eventually revealed, prompting a collected sigh of relief and everyone lives happily ever after.
Polly is the poor little rich girl among a circle of vacuous, boy-crazy young ladies at the finishing school. They speak in frightfully posh accents and come out with lines such as "I've got to chat with my chums", "Isn't she the limit" and "How divine!"
But even today The Boy Friend has plenty going for it. Hugh Durrant's sets - Mme Dubonnet's villa, the seafront and the ballroom - are sensational, the costumes are little short of breathtaking and the dancing is superb.
Director Martin Connor presents a traditional show, in three acts with two intervals. There is a very strong cast, with Rachel Izen slotting in effortlessly as Mme Dubonnet in place of Liliane Montevecchi (broken foot) on the night I saw it.
Zoe Curlett, who has appeared in the West End as both Cosette (Les Miserables) and Christine (Phantom of the Opera) is charming without being sentimental as Polly Browne while Sophie-Louise Dann is a cheeky, endearing Hortense whose French accent is impeccable.
The star of the show though is Roy Barraclough as the dotty, lecherous Lord Brockhurst. He is extremely funny not only in the way he delivers his lines but also in his body language. He is a revelation for those who know him only as Alec Gilroy from Coronation Street; his performance echoes some of the wonderful routines he used to perform with the great Les Dawson.
The only disappointment is Oliver Tobias as Polly's father Percival Browne. Admittedly it is not much of a part but he fails do anything with it and doesn't match the flair nor the effervescence of many of those around him.
The Boy Friend is not perfect: few of the songs are classics, apart from I Could Be Happy With You and Won't You Charleston With Me?; too many of the songs are reprised immediately after they have been sung; and in this production the young ladies of the finishing school appeared far more mature in years than Sandy Wilson intended.
But if you're looking for a gentle, virtuous production which doesn't tax your brain cells, The Boy Friend is a quite ripping evening's entertainment.
The Boy Friend tours until July 12th