I say, I say, I say. Have you heard the one about the wartime baby who grew up full of hope and enthusiasm and became a thorn in the side of the establishment? Stop me if you've heard it Missus but he became lonely and ridiculed.

As a punchline that might not be funny, but James Graham's cracking new play about the life of said wartime baby David Edward Sutch - or Screaming Lord Sutch as he was better known - offers plenty of laughs, interspersed with moments of heartbreaking darkness and despair.

In politics, Graham is on familiar territory – last year's The Vote (broadcast live on election night) had been preceded by The Angry Brigade about an anarchic political group at the Bush Theatre and This House at the National in 2012 about the Labour vote of no confidence. But in Monster Raving Loony he makes sure the audience will Carry on Chuckling as he merges British comedy, politics and the life of our hero.

The fact that we were watching this on the day of the junior doctors' strike, with hints that the government might impose new contracts on the NHS rebels didn't go unnoticed. Sutch had been born in London a year after the war began. As a kid he was full of hope. Everything was going to be different.

Graham displays his playwriting genius by confidently telling his story through a cavalcade of comedy characters. So when his widowed mother pleads with Sutch not to leave home, she is played as a pantomime dame. A farcical version of Confessions of a Window Cleaner and a nod to Hancock's Half Hour are deployed to show Sutch launching a pop career and getting caught up in politics; setting up his own party – The National Teenage Party – to dip his toe in the election water. Just like that.

It's a clever device and the pace doesn't let up – Till Death Us Do Part, Pete and Dud, The Two Ronnies, the one with the glasses and the one with the short fat hairy legs – all landmarks in our comedy lexicon. Catchphrases are anticipated, old favourites are warmly applauded and even snatches of music bring smiles of recognition.

All of which serves to underline the sadness. Because, despite all the jollity and loony policies and lampooning of politicians, Sutch was a sad man. Like other clowns (Tony Hancock, Kenneth Williams) the jollity masked a serious depression. He was a dark person in the darkest corner of Darktown.

Theatre Royal Plymouth's artistic director Simon Stokes is the Captain Mainwaring to this merry band of performers. Samuel James is outstanding as Sutch, barely pausing for breath as he takes the audience from tin plate bashing hysteria to total silence. He is ably matched by the rest of the cast – Tom Attwood, Joanna Brookes, Joe Alessi, Camilla Beeput and Jack Brown. Simply brilliant theatre. I say...

Monster Raving Loony runs at Plymouth Theatre Royal until February 27.