When a new BBC Three comedy made its low-key debut in the spring of 2007, no one imagined that Gavin & Stacey would go on to become the comedic equivalent of a national treasure. 

Despite its two writers’ utter lack of experience as screenwriters – James Corden and Ruth Jones had met as actors on Kay Mellor’s slimming club drama for ITV, Fat Friends – it soon became clear that here was a startlingly original show blessed by a group of fully realised characters, a script crackling with wit and an unusually brilliant cast. 

In other words, pure comic gold that would go on making audiences laugh for three series and two Christmas specials, the most recent (in 2019) attracting an insanely large audience of more than 17 million viewers. 

This masterpiece takes a lot of its humour from the everyday banalities of English – and, it has to be said, Welsh – life. Many of the greatest TV comedies are built around the character of a comic monster. Not so Gavin & Stacey, whose characters, regardless of their flaws, are all rather likeable. Its cheerful optimism is clearly shaped by the pre-credit-crunch, feel-good years of New Labour, when the UK was much more at ease with itself than it is today. 

Corden got the idea after attending a wedding in Wales between a Welsh woman and an English man, which he mentioned to Jones. At the time, he was a young actor whose star was on the up thanks to his part in Fat Friends (which won him an RTS Programme Awards 2001 nomination for Network Newcomer – On Screen) and a role in the original stage production of Alan Bennett’s The History Boys. 

He and Jones sent the BBC a treatment for a one-hour comedy film. “We didn’t even know how to write a ­proposal,” she admitted. “We just wrote lots of dialogue and lots of different characters and little vignettes.” The BBC said it didn’t have a slot for a film and suggested a series charting the relationship and culminating in the wedding. That is how Gavin & Stacey was born. 

Curiously, perhaps, Corden and Jones didn’t choose the title roles for themselves, instead, opting to play Gavin and Stacey’s best friends, Smithy and Nessa. The pair’s on-off, love-hate relationship provides humour and poignancy in equal measure. Had this been a US show, the chances are that Smithy and Nessa would have been conventionally attractive. But us Brits are weird and to show two fat people hitting on one another was ahead of its time. 

Gavin (Mathew Horne) and Stacey (Joanna Page) provide the names for a charmingly twisted romcom with a side order of buddy show: one of the joys of the series is the enduring relationship between Gavin and Smithy, devoted best friends and a pair of likely lads for noughties Britain, when the internet was associated with optimism, and it was cool to shovel down fast food and drown your sorrows in a lake of alcohol. 

Back in 2007, young men rarely expressed their feelings in a comedy but these two Essex lads were surprisingly emotionally literate. Generally, TV comedy thrives on dysfunctional relationships but most of those we see in Gavin & Stacey are warm and loving, despite the friction between Gavin’s Essex tribe and Stacey’s Barry bunch. 

As for the lovers at the centre of the story, Gavin and Stacey’s relationship is not without its trials. Part of the show’s charm is the genuine warmth and innocence of their love. Although here, as with so much of the show, not everything is as it seems when it emerges that Stacey had been engaged five times before meeting Gavin. 

While Corden’s immaculate acting so often steals the scenes, Jones’s Nessa is the oddest and funniest character, a seaside Goth whose past lovers have included Richard Madeley – she was Richard and Judy’s nanny – Prince, John Prescott and Nigel Havers! 

Add in Alison Steadman’s pitch perfect performance as Gavin’s volatile mum, Pamela, Rob Brydon as Stacey’s gauche Uncle Bryn and Larry Lamb as Gavin’s endlessly accommodating dad, and this is a comedy that never loses its freshness. 

Gavin & Stacey is on BBC iPlayer.