How we love old women behaving badly! From Dickens’s Mrs Gamp, through Ealing Studios’ Ladykillers to Monty Python’s Hell’s Grannies, the list goes on.

David Walliams, who now heads the popularity stakes for children’s fiction, has another to add in Gangsta Granny.

Sold by the shelf-load to eager youngsters, the book is now translated to the stage in a musical play destined for a West End run at a venue still to be determined.

Limbering up on tour, the show visits the New Theatre this week to the evident delight of its target audience if not entirely to the satisfaction of adults, this one at least.

But why should grown-ups expect to be amused? Walliams clearly knows his business. If young people are tickled by the spectacle of old ladies feasting on cabbage, with the obvious aural consequences, then of course we must be shown it, repeatedly.

Actually, there is much more to the story, which focuses on an appealing 11-year-old, Ben, expertly played by Ashley Cousins who is clearly much older.

He is the pride and joy of his doting parents (Laura Girling and Ben Martin), although they are ever hopeful that his cherished ambition to become a plumber could be redirected into another area, viz ballroom dancing.

They are (like so many!) obsessed with Strictly Come Dancing, and in mum’s case with one of its male presenters. Parodies of the show punctuate the play, with expert choreography from Paul Chantry and Rae Piper.

Friday night is dance night at their local palais and this means Ben’s delivery into the hands of flatulent gran, with a supper based entirely on ways with cabbage.

It’s a weekly gig he naturally dreads – boring! - until the old lady starts to take on an entirely more interesting character.

Ben’s chance discovery in the kitchen of a biscuit tin packed with glittering diamonds leads on to her confession – he actually catches her red-handed – that she leads a double life as a jewel thief.

Black caped and hooded, she pulls off her heists as the Black Cat, with a mobility scooter as getaway vehicle.

After some persuasion, gran consents to make Ben her accomplice, and together they plan and execute a daring robbery at the Tower of London.

That we should be nice to old people is one message of the play. Another, less welcome, is that theft is OK, provide property is returned.

But let’s not be po-faced about it. This is an evening of good fun, imaginatively staged under director (and adapter) Neal Foster, and with versatile sets by Jacqueline Trousdale, expertly lit by Jason Taylor.

4/5