Spin-offs are a tricky beast. Nail it and you get a Frasier. Go about it all wrong and you've got a Joey on your hands.
So it's perhaps no surprise that for every spin-off that makes it to our screens, there are dozens of ideas that don't. Some of this lot even made it as far as shooting a pilot, before being cast aside by the telly gods.
1. The Daleks
Back in the late 1960s, writer Terry Nation, creator of the Daleks, planned to launch a new series which would see the tyrannical pepperpots battling agents of the Space Security Service.
His pilot script 'The Destroyers' featured the character of SSS agent Sara Kingdom, who Nation had previously introduced, and killed off, in the Doctor Who story 'The Daleks' Master Plan' – so it appears the two shows would have existed in separate universes.
The pilot was rejected by both the BBC and US broadcaster NBC, but Nation's script finally saw life as an audio play produced by Big Finish in 2010.
2. Rose Tyler: Earth Defence
Another Doctor Who spin-off that never was: Billie Piper's companion was supposed to head up her own show after departing the flagship in 2006.
Rose Tyler: Earth Defence would've seen the character working for Torchwood after she ended up stranded on a parallel Earth. The BBC were keen and the budget was allocated for a one-off episode, intended to be the first of a series of specials.
In the end, it was then-Who boss Russell T Davies who pulled the plug, fearing that bringing Rose back so soon would lessen the impact of her original exit.
3. Prison Break: Cherry Hill
Plans were once afoot to make Prison Break a CSI-style franchise, with spin-off Cherry Hill following well-to-do housewife Molly as she's thrown behind bars in a women's prison.
Molly was going to be introduced in the parent show's third season, until the 2007-08 Writers Guild of America strike forced Prison Break to shut down production and rejig storylines, nixing the Molly character and thus her series.
4. Supernatural: Bloodlines
Lucien Laviscount played Ennis Ross, rookie hunter of all things paranormal, in the 2014 Supernatural episode 'Bloodlines' – with the intention that he'd go on to lead his own series.
The new show would have chronicled the war between hunters and monsters in Chicago. The CW passed on the project, while remaining open to the possibility of launching a different spin-off from their longest-running series.
5. Assignment: Earth
Another planted spin-off – or what's known in the business as a 'backdoor pilot' – was Assignment: Earth, a potential sister series to the original Star Trek. The final episode of Trek's second season introduced Gary Seven (Robert Lansing), an alien from the 24th century sent back in time to protect Earth's history from outside interference.
Gene Roddenberry had hoped to devise more standalone adventures for Gary and his team, human assistant Roberta Lincoln (Teri Garr) and... erm... a cat named Isis – but the spin-off never (*cough*) materialised.
6. The Farm
Easily the worst episode that NBC's The Office ever produced, it's easy to see why this backdoor pilot about Dwight (Rainn Wilson) and his family running Schrute Farms failed to spawn a full series.
Instead, the original show wrapped things up neatly with a terrific, touching final episode – no spin-off required, thank you very much.
7. Marvel's Most Wanted
ABC originally began plotting a spin-off from Agents of SHIELD starring Adrianne Palicki and Nick Blood as super-spy lovers Bobbi Morse and Lance Hunter back in early 2015.
The idea was dropped, only to resurface a second time last year with Palicki and Blood being written out of the parent show to shoot a pilot for Most Wanted. ABC eventually passed for a second time, leaving the pair without any show at all. Harsh.
8. How I Met Your Dad
There's another How I Met Your Mother spin-off in the works at the moment, but the first attempt at following up the hit sitcom with the super-divisive ending came in 2014.
Essentially a gender-swapped remake of the original, the How I Met Your Dad pilot starred Greta 'way too good for this' Gerwig as its lead, with Meg Ryan providing a voiceover as the older version of her character Sally.
CBS passed, but the revamped version – more formally titled How I Met Your Father – is still in the running for a series pick-up.
9. Ripper
Angel is one of the few examples of a spin-off that equalled and at points bettered its predecessor, so it's no surprise that there was talk of further series set in the Buffy-verse.
A series following rogue slayer Faith (Eliza Dushku) and TV movies featuring Spike (James Marsters) or Willow (Alyson Hannigan) were all considered, but Ripper was the most enduring possibility.
Anthony Head would've reprised his role as Rupert 'Ripper' Giles in the series, pitched by its star as being like "Cracker with ghosts". Joss Whedon wrote a two-hour pilot film, which was in serious development at the BBC and almost reached the screen twice – once in 2001 and again in 2007.
But Ripper failed to materialise both times, and Head told us in 2015 that he now thinks he's too old to play Giles again. ?
10. Springfield
Remember that brilliant Simpsons outing '22 Short Films About Springfield'? The one with Steamed Hams, the giant man in his tiny car and Chief Wiggum doing Pulp Fiction?
The success of the episode, which focused on Springfield's other residents outside of the Simpson clan, almost led to a spin-off, as former showrunner Josh Weinstein told Digital Spy.
"We felt at that time – around season seven – that we all knew the family so well, so let's start exploring all these great side-characters," he explained.
"It would be a chance to tell full stories about these other characters, but that never happened. I think it could've been great, but everyone was so busy at the time."
