Before starring as the fifth incarnation of television's favourite Time Lord, Peter Davison was a character actor. He got his big break in 1978 when he was cast as Tristan Farnon in drama All Creatures Great and Small Alongside Christopher Timothy and Robert Hardy, and his first foray into sitcom was Marks & Gran's Holding The Fort in 1980, alongside Patricia Hodge and Matthew Kelly; a sitcom that has, inexplicably, never been made available on home media.

Holding The Fort and Sink Or Swim both started in 1980, and for the last two series of the latter he was filming concurrently with his opening series of Doctor Who.

Writer Alex Shearer had created just one previous sitcom, Chalk And Cheese. Broadcast in 1979, it was adapted from an earlier one off play and was written as a vehicle for Michael Crawford, who was coming off the huge success of Some Mothers Do 'Ave 'Em. Crawford was eager not to be typecast as Frank Spencer, and this series saw him play a bearded, sexist Cockney chancer - worlds apart from the infantile Frank. Audiences did not take to the character, and it was cancelled after a single series.

Sink Or Swim (BBC One) followed the misadventures of brothers Brian and Steve, as played by Davison and Robert Glenister. The show was Glenister's television debut in a leading role.

The series starts with Steve, having been sold an idealistic view of London by Brian, moving there from the North (although location filming took place in Bristol) to join his sibling. However, upon arrival he quickly discovers that Brian bent the truth somewhat and is actually a petrol station attendant living in a tiny, squalid flat, from which they are quickly evicted. The first episode sets up the series as Steve finds them a bedsit to share.

The most enjoyable thing about Sink Or Swim is the chemistry between Davison and Glenister. In his autobiography, Davison writes about how they got on famously and would frequently be unable to get through scenes due to uncontrollable laughter, citing one particular sequence in the Christmas special.

The brothers' bickering forms the backbone of the comedy: Steve's oafish masculinity clashing with Brian's gentle demeanour. While Davison has arguably been pigeonholed as an affable figure throughout his career, it is Glenister's portrayal that truly surprises, bringing genuine affability to a character who could very easily have been played as a brutish bully. In fact, it has to be said that Glenister is given some particularly unforgiving dialogue laced with homophobia, but it is a credit to his performance that, despite this, Steve is more man-child than malicious.

Much like Roy Clarke, Shearer's comic voice is gentle. His characters speak in badinage and whimsy. Take Steve's description of his love life:

"I get so little traffic round my erogenous zones, you'd think there were double yellow lines on them."

Sara Corper rounded out the cast as Brian's headstrong, vegan girlfriend Sonia, with whom Steve frequently clashed. Corper previously appeared in an episode of The Jim Davidson Show penned by Shearer, and he gets good mileage out of the comic contrast between her outspoken worldview and Brian's meek meanderings. Though other actors did appear, including Amanda Orton, Briony McRoberts, Gillian Taylforth, Ron Pember and Russell Wooton, the show rested on the shoulders of Davison and Glenister.

Perhaps the biggest issue that faced Sink Or Swim was its lack of identity, with an almost complete absence of plot or overarching storylines. Various threads are pursued through the series but they don't ever really come to anything. There's a search for their estranged mother, their failed attempt to start a boating business, Steve's dalliance with the daughter of a work colleague in Series 2 and even a change of scene in Series 3, when Brian goes to university in Newcastle taking Steve and Sonia with him.

The show also boasts a theme tune from sitcom veteran Ronnie Hazlehurst, the man behind the iconic opening tunes to the likes of Last Of The Summer Wine, Yes Minister and Sorry!. For Sink Or Swim, he opted not to compose an original tune, but instead arranged an instrumental version of The Hollies' 1969 hit He Ain't Heavy, He's My Brother.

In many ways, Sink Or Swim was a victim of circumstance. In 1981, the year after the show premiered, Only Fools And Horses launched on the BBC. Although it took time to build the huge audience figures it would go on to receive, the similarity in concept - two brothers sharing a flat in London - meant that Sink Or Swim fell by the wayside as Only Fools And Horses's popularity grew. Gareth Gwenlan, the producer of Sink Or Swim, went on to produce Only Fools And Horses in 1988, and further mixing the two worlds, Nicholas Lyndhurst starred in Alex Shearer's next sitcom, The Two Of Us.

Indeed, Shearer wrote a number of further sitcoms, including the now completely forgotten The Front Line, perhaps most notable for giving a leading role to Only Fools And Horses actor Paul Barber as one of two brothers - the other being a Rastafarian - who share a house. The series was praised at the time for being one of only a small handful of comedies to revolve around the black British experience, following in the footsteps of The Fosters and coming the year after No Problem!. It did receive some criticism for the accuracy of its depictions however, perhaps not especially surprising with Shearer being a white writer.

Sink Or Swim would not be Shearer's only brush with a Doctor Who actor either, as Patrick Troughton appeared in the first series of The Two Of Us. There would be one further Who connection, as Davison and Glenister reunited on screen in the final adventure of his era, The Caves Of Androzani.

Davison also continued to appear in sitcoms like Eric Chappell's Fiddler's Three and Roy Clarke's Ain't Misbehavin'. To date, his final sitcom role saw him star alongside his daughter Georgia Tennant in Michael Aitkens's 2007 comedy Fear, Stress And Anger. Glenister later found fame as fixer Ash Morgan in long-running crime drama Hustle, while Corper reunited with Jim Davidson for Up The Elephant And Round The Castle, as well as appearing in Roy Clarke's Mann's Best Friends and Norman Lovett's cult curio I, Lovett. Her last credit to date was playing Rab C Nesbitt's snob of a sister in law, Phoebe.

The blurb of the DVD released by Network in 2016 described Sink Or Swim as a "well-remembered BBC sitcom". This may be stretching the truth a little, especially given how long it languished, unseen in the vaults for over thirty years, but there is nostalgic and historic value to the series, and not only as the point where Davison transitioned from character actor to Time Lord. Ultimately, Sink Or Swim is a gentle snapshot of the early-eighties, and the easy chemistry between Davison and Glenister is the glue that kept the series together.