Irish actor Lorcan Cranitch is to join Amanda Redman and Manouk van der Meulen, who play his mistress Prudence and his estranged wife Kaatya, under the covers.
But the explicit content of Deborah Moggach's north London saga is simply a taste of things to come. The Broadcasting Standards Commission has announced that it is loosening its grip on the whole sex question and, as a result, nude bedroom scenes are likely to be broadcast in greater number than ever before.
The revised code on standards of taste and decency in broadcasting, published on Friday, reflects a change in attitude among the commission's influential panellists. While the 9pm watershed - the earliest in Europe - is to be preserved, and potentially even strengthened, sex scenes are now considered more acceptable.
A statement from the commission explains: "[Our] research indicates that audiences in Britain have become more relaxed about the portrayal of sex."
While this new assessment of public opinion has incensed members of the National Viewers and Listeners Association, it does appear to have some basis in fact. The viewer has become inured to nudity in screenplays. It is crucial ammunition in the battle to win weekend audiences and, as a result, Sunday night drama often centres on a sexual theme. Coincidentally or otherwise, today's raunchier series also tend to be set in north London: Close Relations itself, Tears Before Bedtime, a BBC1 Sunday night drama series about nannies, and the notorious The Men's Room, featuring Harriet Walter and Bill Nighy in simulated oral sex.
Back in the 1950s the BBC felt it necessary to ban jokes about honeymoon couples, chambermaids, fig leaves and ladies' underwear. More bizarrely, mention of lodgers and commercial travellers was also frowned upon. Things have changed. Staff at the offices of Right to Reply, the Channel 4 television watchdog programme, confirm that so far they have received no letters of complaint at all about Close Relations, in spite of a ground-breaking lesbian love scene in an earlier episode.
In 1986, however, many Sunday evening viewers were outraged when the actor Patrick Malahide's bare rump was seen rising and falling in the middle of the Forest of Dean for a record 11 minutes in Dennis Potter's The Singing Detective. Albert Finney's lustful advances on two women in The Green Man also provoked criticism, and in 1993 enraged licence-payers wrote to complain that lengthy sex scenes between Sean Bean and Joely Richardson in the BBC's Lady Chatterley had put a dent in their weekend. Since then tolerance both of sexual diversity and of the sex act itself appears to have grown.
John Beyer, general secretary of the Viewers and Listeners Association, concedes that the strictures of the past were excessive, but he disputes the idea that viewers are no longer offended by sex on their screens.
"What the commission is saying about sex now lacks all definition," Mr Beyer said. "We tell those who contact us to complain in reference to the terms set out by the commission, but if they are entirely vague there is no way of doing so. Their own survey figures have indicated that 41 per cent of people are offended by explicit scenes."
The history of shock-drama has to start in 1967 with The Forsyte Saga and the brutal rape of Irene by her husband Soames. Andrea Newman's Bouquet of Barbed Wire was the next to cause upset a decade on with its treatment of the subject of incest.
Anthony Sher's character in the adaptation of Malcolm Bradbury's The History Man was probably the small screen's most prolific sexual athlete, while Gemma Craven's lipsticked nipples caused excitement in 1978 in Potter's Pennies From Heaven. Not all these series went out on Sundays - some went out on Wednesdays, providing a mid-week top-up of explicit sexuality.
A spokeswoman for the BBC Drama department said that the corporation did not set out to offend or to substantiate the idea that Sunday's viewing is sex themed. "While Close Relations suits the late Sunday drama slot," she said, "it would not have been commissioned with that specifically in mind. Every incident of sexually explicit material is judged separately and on its own merits according to our Producers' Guidelines."
She said that BBC drama would not increase its sexual content as a result of the revised code but would "continue to be challenging in this area".
Scriptwriters are no doubt already struggling with fresh sexual permutations.Reuse content