Porridge originated as one of seven pilot episodes in the BBC's 1973 project Seven of One, designed to showcase Ronnie Barker in different sitcom formats, with the most successful pilot developed into a full series.

Ronnie Barker initially preferred another pilot, a sitcom about a Welsh gambling addict, over 'Prisoner and Escort', but the prison-based pilot was ultimately chosen for a full series.

The title 'Porridge' was arrived at independently by Barker, Clement and La Frenais, all coming up with the same 1950s slang term for a prison sentence.

Writers Dick Clement and Ian La Frenais researched the show by consulting former prisoner Jonathan Marshall, author of 'How to Survive in the Nick', who advised them on prison slang, dress and routines and inspired the show's 'little victories' theme.

Ronnie Barker suggested actor Paul Henry for the role of Lennie Godber, but the production team instead cast Richard Beckinsale.

The Home Office refused permission to film inside or outside a real prison, forcing the BBC to use the gatehouse of a disused prison in St Albans for the opening credits and other substitute locations like Leavesden Hospital and a site near Ealing.

Production designer Tim Gleeson converted an old water tank at Ealing Studios, previously used for underwater filming, into a multi-storey set to depict the wider prison interior.

Filming for the second series' exteriors at Leavesden Hospital was stopped after complaints from patients' families, forcing production to move to another institution near Ealing for the third series.

Unlike the TV series, the 1979 feature film was shot entirely inside a real prison, HM Prison Chelmsford, which was temporarily vacant following a fire.

Instead of theme music over the opening credits, the show used a booming narration by the sentencing judge, voiced by Ronnie Barker himself, though Barker later said he regretted recording it; the judge role was later played by Maurice Denham in two third-series episodes.

The closing theme music was written by Max Harris, who deliberately gave it a cheery music hall feel to contrast with the show's dour prison setting, reflecting Fletcher's Cockney origins.

The show popularised the word 'naff' as a stand-in for stronger swear words, a term that had been virtually unknown before Porridge; Ronnie Barker later admitted in a 2003 interview that he did not actually know what the word meant.

The series coined the genuine neologism 'nerk' as a softer alternative to 'berk', and also used the term 'scrote' to mean an unpleasant person.

The first episode attracted a television audience of more than 16 million viewers when it aired in 1974.

According to ex-prisoner and Guardian columnist Erwin James, Porridge was hugely popular among real British prisoners, who considered its depiction of the relationship between inmates and prison officers remarkably authentic.

Comedian Peter Kay, a fan of the show, was offered the role of Fletcher for the 2009 stage adaptation but turned it down; the part went to Shaun Williamson instead.