Spike Milligan’s wearying zaniness could be off-putting to the unconverted and that form of humour sometimes jars, although only very occasionally, in this madly spirited and delightfully baggy show based on Spike’s wartime memoirs.

The play takes the form of a wartime concert party, with sketches and musical numbers woven through scenes from the books, played as if they were skits.

We begin with Spike arriving three months late for military service in 1940, having ignored all those ‘invitations’ posted to his home. He offers to atone for his tardiness: “I’ll make up for it – I’ll fight nights as well.”

This sets the tone for Spike’s confrontations with authority, his immersion in the craziness of war, and the mental collapse that would mark his life, and help to create a form of comedy that inspired the likes of Monty Python.

In the books, and here on stage, Spike had an enjoyably sharp ear for the absurdity of officialdom, such as the sergeant major who booms: “Silence when you are speaking to an officer.”

Spike bounces from experience to experience, coping with extreme tedium (98 per cent of war, as someone observes) and the sheer bloody terror (two per cent), while forging the strong friendships of young men trapped in khaki-cloistered lives. He has, in a stand-out performance from Sholto Morgan, the bewildered air of a man buffeted by confusion, and armed with the best form of self-preservation: a sense of the ridiculous. Morgan, in his first professional engagement, summons up just the right head-scratching befuddlement and wandering wit.

If the first half takes time to find its pace, the second is magnificently funny, wildly inventive, riotous and enjoyably barmy. The adaptation by Ben Power and Tim Carroll is clever and economical in the way simple props are used to convey many situations, not least the hospital bed to which Spike is confined suffering from piles. This requires the actor to stand up when he would normally be lying down, and then to bend forwards from the vertical when ‘sitting up’ as visitors plonk themselves on his bed.

There is also a good visual gag reminiscent of Buster Keaton that it would be a shame to divulge.

The cast of five – Morgan is supported by Matt Devereaux, William Findley, Dominic Gerrard and David Morley Hale – spurt through assorted characters and scenarios with remarkable virtuosity, especially as most of them play musical instruments as well.

In short, this is a fun and riotous show with flashes of poignancy showing through the bonkers behaviour.

*Adolf Hitler: My Part In His Downfall, York, Theatre Royal, today 2pm and 7.30pm, tomorrow 7.30pm, Saturday 2.30pm and 7.30pm. Box Office: 01904 623568.