INTRIGUED I am.

It was announced at the weekend that there is to be a Star Wars spin-off movie, called Rogue One. It will tell the story of a mission by a group of resistance fighters to steal plans to the Death Star, and there are strong rumours that Yoda in it will be. And that's the last time that joke I will do. Promise.

My first reaction when I heard that a spin-off was coming to a galaxy near us was much the same as it is whenever sequels and prequels are first mooted: to wonder whether it wouldn't be better to concentrate scarce resources on developing original ideas rather than constantly trying to milk old ones. But then came the realisation that, actually, especially in the case of television, spin-offs can be pretty darned good, and sometimes even better than the originals.

The classic case in point has to be Frazier, which ran for 11 seasons (curiously, the same length as its parent, Cheers), and won 37 Emmy Awards, a record in American television. That's far from the Norm, and when it finished in 2003, everybody knew his name. It also introduced some sublime characters in its own right, notably the prissy Niles and the carmudgeonly Martin. Incidentally, Cheers had another, lesser-known spin-off: The Tortellis, a sitcom about spiky barmaid Carla's ex-husband Nick and his dimwit bride. It lasted 13 episodes.

A show has to have strength in depth in the first place to be able to serve up more than one appetising platter of offcuts, which brings to mind one of my earliest TV memories: Z-Cars. For the uninitiated, it was a starkly realistic police series which ran for more than 800 episodes. Most of those involved Det Insp Barlow and Det Sgt Watt, who both went on to star in Softly Softly, with the former also getting a good run-out in Barlow and Barlow at Large. Sgt Watt, of course, was played by Frank Windsor, who went on to earn a decent crust selling funeral plans on the back of free carriage clocks.

A decade later, and the twee sitcom Man About the House, about a flatsharing trio, spawned both George and Mildred and Robin's Nest, while across the pond, Happy Days gave us Laverne & Shirley and Mork & Mindy (we shall gloss over the short-lived Joanie Loves Chachi).

The spin-off flood has continued unabated ever since: I give you Dallas/Knots Landing; The Six Million Dollar Man/The Bionic Woman; Porridge/Going Straight; Doctor Who/Torchwood/The Sarah Jane Adventures; and the latest, Breaking Bad/Better Call Saul.

I note there was talk recently of spinning off Kat and Alfie Moon from EastEnders. Sorry, but that's going too far.