But all is not as it seems, according to Geoffrey Perkins, the BBC's head of comedy. Speaking down the line from the Montreux Festival - where every self-respecting comedy exec hangs out at the end of April - he mounts a robust defence against the accusation that the BBC has run out of ideas. "I have no doubts about doing these shows," he contends. "The key thing is to view them as individual shows, rather than as some mad strategy to bring back old sitcoms. It's not a question of `let's pick up the back catalogue and see what more mileage we can squeeze out of it'. It's just a coincidence they're both coming out this year. The Liver Birds has been talked about for years and years, and David Nobbs, who's almost my favourite writer, just came up with the idea for Reggie Perrin."
The idea - which has become The Legacy of Reginald Perrin - is that the eponymous hero has been killed by a falling billboard, advertising the insurance company he was with. His surviving friends and relatives - including wife Elizabeth (Pauline Yates), brother-in-law Jimmy (Geoffrey Palmer) and boss CJ (John Barron) - are only able to inherit his substantial legacy if they can prove to the executor of his will (Patricia Hodge) that they have done something truly absurd. "It is, of course, an absurd idea to bring the series back," Perkins comments, "and that's precisely why we're doing it... As David Nobbs puts it, `Reggie Perrin is back, and this time he really is dead'. You take a deep breath and say to yourself, `OK, will this get viewed as a cynical exercise?'. But I think it's a very strong idea in its own right. Reggie Perrin as a character still dominates everything, because it's all caused by his actions."
Nobbs, whose original series ran between 1978 and 1980 and recently enjoyed a repeat run, expands on the theme. "I didn't get where I am today by looking backwards, so it was a great surprise to me when I suddenly realised that I had thought of an idea for a new Reggie series. Even then, I wouldn't have written it if I'd thought that there was a risk of spoiling the memory of the original with something of less quality. The Legacy of Reginald Perrin is about the large number of old people in our society and about redundancy and insecurity in the workplace, and I believe it is as relevant to the 1990s as the originals were to the 1970s."
The return of The Liver Birds has been under discussion almost since the show came to the end of its 10-year, 100-episode run in 1980. "This is a good time to do it," Perkins declares, "because now the world is different and the characters are different. Their position has changed so fundamentally, it's almost a new show. If you'd brought it back 10 years ago, it would have been closer to a continuation. Now there's a great time leap."
Carla Lane at first turned down the BBC's pleas for an updated Liver Birds. "I was worried people would think I didn't have any more ideas left," she recalls. "But what finally convinced me was one of the Big Three at the BBC saying to me, `The thing I love about your work is the pain'. With two 50-year-old women who were once ravers, there's a lot of pain. There's a lot of poignancy in the passing of time. I decided not to make the girls tremendously successful. I wanted people to identify with them."
Like a female Victor Meldrew, she prides herself on being "TV's Ms Misery". "I've been concerned at the recordings [of the new Liver Birds]," she continues, "and have had to say to the producer, `there's too much laughter here, it's got to stop'. I'm a miserable comedy writer. I try to bring comedy up to the status of drama - and in order to do that, you've got to have a few tears as well. I build characters very carefully and make them sad rather than laugh-a-minute. The writing must be thoughtful and leave a mark. My message is that life is shitty."
It has certainly become so for the once young, free and single Sandra (Nerys Hughes) and Beryl (Polly James). In the new series, they have gone from mini-skirts to the menopause. Sandra has divorced and is left looking after her snobby mother, while Beryl has divorced and is left looking after a delinquent son. "It's not as if I've got hordes of rampant lovers scaling the drainpipes," Sandra sighs. "Sometimes I feel like a dead flower."
Despite the wistful air of the new Liver Birds, Lane is still anticipating the worst from the critics. "I don't expect anybody to say, `wasn't that great?'. I expect them to say, `that was awful'. Critics are really cruel to me. I was referred to as `the BBC's sacred cow' the other day."
These revivals at the BBC may not be too encouraging for new comedy writers ("where will the new Nobbs and Lane come from?" they might ask) but Perkins assures me that there are "six or seven new shows" nestling alongside these two comeback kids.
"There are specific reasons to do these two," Perkins concludes. "We're not going to work our way through the back catalogue. I've had people coming to me saying, `What about bringing this show back?', [he is too discreet to say which], but now it would be difficult to do any more. Unless of course John Cleese came to me suggesting we re-do Fawlty Towers..."
`The Liver Birds', Mon BBC1 8.30pm; the original series is on Fridays UK Gold 2.15pm. `The Legacy of Reginald Perrin' will be broadcast in the autumn