This Is Jinsy. Welcome...

Recently there's been a trend in British comedy for very straightforward sitcoms set in homes in England in the present: Friday Night Dinner, Grandma's House, Him & Her. Jinsy is a long, long way away.

"The fact that it can't be compared to a lot of things probably helps," says co-creator and co-star Chris Bran on set, as he waits to be called for his next bit of filming. "It's its own thing." We're in a smallish TV studio in a deeply unglamorous part of west London. Bran's got quite a lot of waiting to do today, because the star of this morning's scene, a goat called Gobo, keeps running out of shot.

Over Bran's left shoulder are a gaggle of elderly, bearded extras, hired by the production team from a specialist agency. Behind him: a wicker drum kit with fur trim.

Chris Bran and Justin Chubb have been making odd things together since they were kids growing up on Guernsey: songs, films, books full of fanciful drawings. Via a process nobody can quite explain, last year they and rookie producers James Dean and Chris Carey landed a half-hour pilot on BBC3, which Chubb and Bran wrote, designed, directed, edited and starred in themselves. Some idiot at Radio Times called it "as infectiously funny as a badly stuffed owl".

Niche work if you can get it
Safe to say This Is Jinsy has always been destined for cult appeal. Any more is now impossible anyway, because of where it's ended up. Having shown the pilot, BBC3 declined to commission a series – whereupon its former controller Stuart Murphy, now charged with masterminding Sky's efforts to become a major player in British TV comedy, stepped in.

But unlike Trollied, The Gates, Stella, Spy and Murphy's other new comedies, all of which are properties of the flagship entertainment channel Sky1, This Is Jinsy is being shown on Sky Atlantic – a channel otherwise full of glossy HBO dramas, only available to Sky subscribers.

Of the decision to put Jinsy on Atlantic, Sky says: "Sky 1 HD is committed to broad, populist entertainment and comedy on the channel should be just that. This Is Jinsy is a creatively riskier premise - brand new talent, left-field writing, bold characters and a brave new world. It's the perfect fit for Sky Atlantic's first comedy commission."

"Hopefully the evening on Sky Atlantic won't dip from Boardwalk Empire to Hi-de-Hi!," says Chubb. "Hi-de-Hi! was good, don't get me wrong. But that's what's heartening about all [This Is Jinsy's] brilliant design work. It will look really filmic."

It will indeed: like all the other comedies in Sky's new roster, This Is Jinsy has been shot in HD. And it's undergone a makeover. Bran did all the post-production on the BBC3 pilot himself, despite his near-total lack of experience. Now, although the island's curious vistas are still created entirely using green screens, hence the unglamorous indoor shoot, there's a full production team bringing Chubb and Bran's silly visions to life.

"You've got to be careful what you draw," says Bran, deadpan. "The props and costume departments will make exactly what you draw. They go off and make it and we're like no, that was a joke! It's quite a responsibility. But people couldn't see how you could wear a cupboard, for example, until Justin drew it."

A twist of limelight
At a time when the BBC is stifling creativity with reduced budgets and risk-averse red tape, Sky is acquiring a reputation for giving writers the freedom and the money to make exactly the programme they want. (One Sky exec describes This Is Jinsy as "the sort of thing the BBC should be making, but isn't".) Reduced ratings are the pay-off – even on Sky1, but more so on Sky Atlantic, where This Is Jinsy will be doing incredibly well if it can attract half a million viewers. Sky's policy of ring-fencing Atlantic to drive up Sky subscriptions means This Is Jinsy might not even get a repeat on Sky1.

Yet the combination of an intriguing pilot episode and Sky's big cheque book has enabled the show to hire impressive guest stars. Under the direction of Matt Lipsey (Little Britain, Psychoville), big names like Harry Hill, Peter Serafinowicz, Catherine Tate and Jennifer Saunders are all involved.

"We just wrote the parts by ourselves as usual," says Chubb. "Then when the casting director came on board it escalated to a level we never thought we could achieve."

First up is the most famous of them all. In the opening episode, David Tennant extends his wide acting range quite a bit further by playing TV presenter Mr Slightlyman. The story centres on Jinsy's approach to matrimony: forced temporary marriages, with Jinsymen and Jinsywomen regularly re-paired via a televised lottery. Mr Slightlyman, a whiningly camp, brutally primped stick insect of a man, is the host.

If Tennant's sex-symbol status can survive Slightlyman's orange hair, mustard jacket, dayglo paisley leggings and stack heels, it can survive anything – but Tennant gives it his all.

"Having a pilot and scripts to show people meant actors could feel fairly safe. They knew what they were doing," says Chubb. "What I've loved about the cameos is that people have approached them as proper characters. Not just: oh, I'll do a silly voice. David said, 'I'm quite nervous.' I thought, what? We were thinking, is everything all right? Will he enjoy it?"

Did they have a problem convincing him to wear the outfit? "No... the problem was getting him out of it."

The old ones are the best
This Is Jinsy arrives having created a distinct world, visual and verbal, and its virtually unknown creators have the confidence to do that despite being out of step with contemporary TV. It's been over a decade since a comedy fitted that description... “It is a bit like The League of Gentlemen,” Chubb acknowledges, “but with less murder and more songs.”

In fact Jinsy is a much softer, sillier place than Royston Vasey, with a very traditional vibe beneath the costumes, the cutaway sketches and the wormwoody weirdness. Ask Chubb and Bran for more of their touchstones, and the answer is almost comically retro.

“I hope This Is Jinsy will have a Goodies-type impact – that children will love it,” offers Chubb. “But also that the older Python audience will like it... the Milligan fans.”

As I pause to wonder how Sky's marketing department will reach out to that key Spike Milligan demographic, Bran tops Chubb by naming his key influences, almost all of which are more than 40 years old. “Here Come the Double Deckers! The way they got into their den by pulling wires and wheels. Oliver Postgate. Spike Jones and the City Slickers, they're very Jinsy. I had a whole VHS of that as a kid. I love Laurel and Hardy as well. I was quite disappointed when I realised they were actors when I was eight.”

"Children still love Laurel and Hardy," adds Chubb. He and Bran are hopeful that This Is Jinsy will appeal to kids, despite its scary oddness. "The scary element is good," Chubb goes on. "Children want to be safely scared or intrigued by things. I felt that with Python. In the 70s there was a lot of spooky, eerie children's TV – like Children of the Stones. You get this incredible excitement with things that are not our world. They go in much deeper. What you watch when you're younger is what goes into your psyche."

La, la la la la la la, la la la la la la
"We were both in bands as kids," recalls Bran. "That was our common thing." One of the first things that stands out about This Is Jinsy – that makes you feel you're going to love it, not just like it, and that you'll want to watch it over and over – is the music. Like Flight of the Conchords, the songwriting is quietly excellent, with catchy melodies and spot-on genre parodies underpinning the stupid lyrics.

“We could do an album, like Flight of the Conchords,” says Chubb, “but all our songs are 41 seconds long. Perhaps an album with 107 tracks on it. Doing a short song is like telling a joke. Timing, rhythm and bad hair.”

It's not just songs that set This Is Jinsy apart, although uncomfortable folkster Melody Lane (Chubb in drag) is one of the series' best characters. Each week's story is peppered with barely relevant skits: talking seagulls swapping awful puns; an old ladies' tea room that inexplicably has two commentators describing the action; a talent contest judged by a dog. There's also Pameric, Jinsy's period drama which is a huge hit on the island despite continuity problems that make Acorn Antiques look like The West Wing.

All that said, at the programme's heart is a textbook sitcom duo. Chubb plays Maven, the island's "arbiter", who's second in command only to Jinsy's unseen, possibly inhuman overlord, the Great He ("Jinsy praise him!"). Maven is vain, fussy, dressed in ludicrous shorts and blessed with Chubb's snaggly teeth.

"Maven's a deluded character who wants to control his and the larger world and is completely unaware of his impotence," says Chubb, who delivers all Maven's lines down his Kenneth Williams nose with a shiver of frustration.

Maven and his assistant Sporall are co-dependent opposites: Sporall, played by the better-looking, softer-spoken Bran, is clever but powerless, and the only character who realises that Jinsy is a thoroughly bizarre place. "Sporall's the classic normal person among it all," says Bran, ignoring the fact that he's wearing a false beard decorated with three upside-down seagulls on sticks, because the episode they're filming features Sporall entering Jinsy's beard pageant.

On Jinsy, the most normal person in the land isn't that normal.