Porridge was the best of the Beeb's 2016 season of 70s sitcom revivals. That really is damning this sequel with faint praise, as they were universally dreadful. Now back for a full series, Kevin Bishop stars as Fletcher's grandson Nigel, behind bars for unspecified cyber-crimes, a fast talking cheeky chappy offering advice for a price to the other inmates.

He might run rings around the other cons and screws but he's nowhere near as smart as he likes to think, being often hoisted with his own petard. In the opening episode his letter-writing scheme quickly spirals out of control when he falls for another inmate's girlfriend.

Porridge really was one of the jewels of the golden age of British sitcoms. Shows like It Ain't Half Hot Mum and Are You Being Served have aged badly, but Porridge featured Ronnie Barker's finest performance, the prison setting gave it an edge and wistful melancholy.

Mark Bonnar does a decent enough impression of hard-line screw Mackay (so memorably played by Fulton Mackay), while Dominic Coleman slips into Mr Barrowclough's (Brian Wilde) shoes as lenient Officer Braithwaite. It must be a daunting task stepping into such an iconic role. Inevitably Bishop pales in comparison to Barker's Fletch. Barker mined a hangdog fatalism, Bishop is just cocky. Without an innocent in the mix (there's no equivalent of Richard Beckinsale's Godber), the entire set up feels unbalanced.

40 years have passed and, perhaps unsurprisingly, Porridge 2017 feels dated, the jokes old fashioned and heavily sign-posted. We aren't trusted to fill in the blanks, the perfect example being Officer Meekie (Bonnar) literally telling Fletcher, and less observant viewers, that the plot to the first episode resembles Cyrano de Bergerac.

It's amazing that original writers Dick Clement and Ian La Frenais (both now 80) are still on board. It gives Porridge 2.0 a wonderful sense of continuity. However, without Barker it really should have been left locked in the vault untouched for posterity.

Porridge starts on BBC One, Fri 6 Oct (time tbc).