Tonight, hundreds of thousands of Archers fans will be glued to their radios, agog to hear the climax of a storyline that has shaken their faith to its foundations. Ruth, who, as the wife of David Archer, is the series' matriarch-in-waiting, will be wrestling with her conscience and, quite possibly, with Sam Batton, who has booked a hotel room in Oxford with the intention of consummating their illicit love. Will she throw aside 18 years of happiness, the welfare of her three children, her share in Brookfield farm, and all vestiges of plausibility, to play Madame Bovary with a cowman? Or will sanity prevail, and Ruth head back to dowdy contentment?
For many regular listeners, though, the need to know how this bit of plotting turns out will be mixed with simmering resentment at the way the characters have been manipulated to maximise publicity. Ruth's uncharacteristic tumble into the clutches of lust has been timed to coincide with the programme's 15,000th edition - a fact that may cut some ice with journalists and the BBC, but that matters not a whit to most of its audience.
In recent weeks, Ruth and Sam's affair has prompted vociferous complaints about its plausibility, on BBC online forums and to the Radio 4 programme Feedback. When Vanessa Whitburn, editor of The Archers, appeared on Feedback to defend the storyline, she made the mistake of seeming to patronise the complainers, saying "Bless 'em" - thereby stirring the pot even more.
The row is one more instance of the BBC's failure to grasp the peculiar nature of the relationship between The Archers and its loyal listeners. For Archers fans, more than the fans of any other soap, the programme exists in a nether dimension, suspended between fact and fiction. That fact is partly a byproduct of sheer longevity - as the 15,000-mark confirms the programme is by far the longest-running drama serial on any medium, anywhere in the world. Few of its listeners can remember a time before it was there, or even before it was familiar; over the decades, listeners become intimately acquainted with the characters. The sense of reality is sharpened by the medium: David and Ruth, and all the other regulars, travel with you in your car, bustle around with you in your kitchen as you prepare your evening meal, wallow with you in your bath; they inhabit corners of your life in a way that television characters never can.
Having begun in 1950 as a local programme, intended to impart agricultural advice to Midlands farmers in a palatable form, The Archers soon transcended those limited beginnings, to create a universe of its own. For Archers listeners, the topography of the Midlands county of Borsetshire is as familiar as many real places. There is Ambridge itself, the hub of all Archers activity, with the pond, the village shop, The Bull, St Stephen's church, the bucolic loveliness of Honeysuckle Cottage and the slightly rougher charm of the Glebelands housing estate; beyond lie the villages of Penny Hassett and Loxley Barrett, the railway line at Hollerton Junction, the shops of the county town, Borset; and beyond, Felpersham, with its cathedral.
It is easy to find yourself an unwitting resident of this world. I write from a knowledge painfully acquired, having been brought up on The Archers from an early age - my childhood traumas include the memory of Paul Johnson, first husband of Christine Barford, failing in his fish-farm venture and absconding mysteriously to Hamburg, where he later died in a car crash. (Road accidents are Ambridge's most popular way of disposing of superfluous characters: other victims over the years have included Polly Perks, first wife of local pub landlord Sid Perks, Mark Hebden, first husband of David Archer's sister Shula, and John Archer, their cousin, who died under an overturned tractor.)
That all happened in 1975, when I was 10. Not much later, I remember being engaged in an earnest discussion over the dinner table with my mother and sisters about Shula's fling with Simon, editor of the local paper, the Borchester Echo. My father, more practically minded than the rest of us, tried for a few minutes to work out who we could be talking about, before the penny dropped and he exploded: "These aren't real people! It's that bloody programme again."
Over the years, the BBC has misunderstood or abused that bloody programme's special status time and time again. In the 1980s, it promoted a tee-hee ironical relationship with the real world, importing a variety of real-life guests stars to Ambridge. At one point, Radio 1 DJs held their annual Christmas dinner at Grey Gables, the swanky hotel run in those days by local magnate Jack Woolley; John Peel turned up at The Bull, to be importuned by local Jack-the-lad and would-be country-music star Eddie Grundy: later, Peel played Eddie's record - "Poor Pig" - on his Radio 1 show. Princess Margaret turned up for a charity fashion show - the room at Grey Gables where she used the toilet was afterwards rechristened the Princess Margaret suite - and Anneka Rice rebuilt the village hall.
This trend reached its nadir in 1989 with Terry Wogan's appearance at the village fete, to mark the 10,000th edition - the event that, more than any other, heralded the end of my own addiction to The Archers. For some years, Pru Forrest had been one of the many silent characters (for some time, The Listener ran a witty cartoon strip by Merrily Harpur entitled "Unheard of Ambridge", fantasising about the private lives of these characters): her taciturnity had become a joke, with scriptwriters competing to invent more outlandish excuses for her failure to speak.
Excited by Wogan's arrival, Pru began to talk, and wouldn't shut up: the big surprise being that she had the voice of Dame Judi Dench. Older listeners, like my mother, who could remember what Pru really sounded like before her non-speaking days, were outraged by this travesty. Younger listeners were irritated at the clumsy corporate attempt to muscle in on an in-joke and make it a news item. More recently, this tendency to blur the boundaries between the real and the fictional has resurfaced again, with appearances by Radio 1 lout Chris Moyles and forgotten fashionista Zandra Rhodes.
Almost as irritating for long-term listeners, though, is the programme's periodic descent from mundane family dramas into melodramatic passion and absurdities of the kind more usually associated with grand opera and the defunct Channel 4 soap Brookside. Last year, Ambridge was shaken by the love triangle of Ed and William Grundy and Emma Carter - while engaged to William, Emma had two one-night stands with his younger brother, Ed; after the marriage, and the birth of a son, she left William for Ed, insisting the child was his. After months of drama Ed vanished, turning up this year, having been sleeping rough, an alcoholic and crack addict. The year 2004 saw the programme's first gay kiss, between Adam Macy and his Irish boyfriend Ian. (This was not the first time Adam had been at the centre of sexual controversy: in the Sixties, he had been The Archers' first illegitimate child, the product of a fling between young hippy Jennifer Archer and cowman Paddy Redmond - what is it about those cowmen that those Archer women can't resist?)
Other scandals have included Sid Perks's saucy shower with Jolene the barmaid (later to become the third Mrs Perks), Brian Aldridge's midlife crisis and resultant child with beautiful young Irishwoman Siobhan, not to mention Brian's previous midlife crises with Mandy Beesborough and Caroline Bone. There has also been an assortment of robberies, arson attempts and unspecified shadiness - the death of Nelson Gabriel, owner of the local winebar, in South America being a recent example.
In some respects, the programme has become tamer in recent years: in the mid-Sixties, Nelson's father, Walter, famous for his cry of "Me old pal, me old beauty", bought an elephant called Rosie; not long before that Tom Forrest, the gamekeeper, whose sister Doris was the reigning matriarch, shot a man and was tried for murder. What is peculiar is the local amnesia about these events: in real life, an elephant and a murder would be the subject of talk for decades; in Ambridge such things are soon swept under the carpet.
But every village has its share of scandals and dramas, and it's arguable that, averaged across time, Ambridge has been an unusually placid place. What grates is not melodrama as such, but melodrama drummed up for an occasion, at odds with the programme's internal reality. The tradition goes back a long way: everybody knows that Grace Archer - Phil Archer's flighty first wife - died in a stable fire purely to steal audiences from the opening night of ITV.
Ruth's affair with Sam is both less blatant and more irritating, because Ruth has been established for years as Not That Kind of Girl. Since her advent in the mid-1980s as an agricultural student on work experience at Brookfield, she has been groomed as a family lynchpin - loyal wife, loving mother, and handy in the milking-shed when called on. To hear her now perform such a volte-face is consistent with human nature; but human nature is the last thing The Archers has ever been about. That is why its fans love it, and why the BBC mucks around with it at its peril.
10 things you never knew about 'The Archers'
* THE EARL Timothy Bentinck (David Archer) was born on a sheep station in Tasmania. He is also the 12th Earl of Portland.
* THE THEME TUNE The Archers theme is called "Barwick Green" and comes from a suite called My Native Heath by the Yorkshire composer Arthur Wood. Written in 1924, a second section, known as the "Doom Music", has been dropped in recent years. Archers editor Vanessa Whitburn is said to hate it.
* THE GRADUATE Felicity Jones, who plays single mother Emma Grundy, graduated from Wadham College, Oxford this year. She will take the lead role of Catherine Morland in ITV's upcoming version of Northanger Abbey.
* THE BIG SCREEN In a scene from Chicken Run (2000), the lead character Rocky is tuning into the radio. One of the snatches of music heard is the Archers theme.
* THE EXPERT Graham Harvey, the agricultural story editor, studied agriculture at Bangor University. After graduating, he worked for Farmers Weekly and as a contributor to Farming Today on Radio 4. He joined the Archers scriptwriting team in 1984 and has written over 600 episodes.
* THE PARODY In 1961, Hancock's Half-Hour parodied The Archers in an episode called "The Bowmans".
* THE AFGHAN VERSION In 1994 the BBC World Service in Afghanistan launched Naway Kor, Naway Jwand ("New Home, New Life"), an everyday story of Afghan folk. It tends to concern unexploded landmines rather than farming techniques, but its model is The Archers.
* THE SCRIPTS The writers each have 14 days to produce a week's scripts.
* THE REPORTER As well as playing Ruth Archer, Felicity Finch is also a radio reporter, and has produced features for Woman's Hour and Home Truths among others.
* THE COMEDIENNE Tamsin Greig (Debbie Aldridge) has starred in a number of TV comedies, including Black Books and Green Wing.
By Andrew Cummins