There are many little remembered film adaptations. 'Father Dear Father', 'Never mind the Quality feel the Width', 'That's Your Funeral', 'For the love of Ada', 'Nearest and Dearest','Man About the House', 'The Likely Lads' etc. Most were awful, some have become interesting curiousities. One of my favourites, although not strictly a spin off, was Dick Emery's 'Ooh You are Awful'.
The Seventies was the heyday of these films, especially after Hammer scored a big success with the 'On The Buses' films. Some, however, like the three Frankie Howerd spin offs, 'Up Pompeii', 'Up the Chastity Belt' and 'Up the Front', according to Ned Sherin the producer, made very little money. Most of these films were critically mauled and found it hard to break out of the thirty minute format, even when the genius of Galton and Simpson was writing them as in the 'Steptoe' films. Thus the laws of diminishing returns put an end to the spin off on the cinema screen. The dearth of really good sitcoms material also didn't help, 'George and Mildred' being one horrific example.
In some cases such was the hunger for material that shows that weren't even that successful got spinoffs; like 'That's Your Funeral' a humdrum sitcom about a funeral parlour starring Bill Fraser and Raymond Huntley that only lasted for one season and wasn't really that popular. It must be said however, that two of the best examples were the last to be made, 'Rising Damp' and 'Porridge'.
In the eighties TV made its own longer specials, 'To Hull and Back' the 'Only Fools and Horses' Christmas Special being the first of many. The same was true of 'Last of the Summer Wine', which started with 'Getting Sam Home'. We may however be seeing a return of the spin off after the success of the 'Inbetweeners', with the dreadful Keith Lemon film out now and a Harry Hill film in the pipeline as well as numerous other comedians working on scripts. But as we know if the quality is not maintained the future won't be bright.
The Young Ones were offered a chance to make a film of the show in the eighties and refused, with hindsight they may have been correct, it is not an easy path to follow and even the most gifted of writers and performers have come unstuck over the years.
Stone me, What a Life!