Britain's most famous radio village ready to shake its fans to the core...

The producer who's been at the helm of the Radio 4 show for the last 20 years has chilled the hearts of some of its five million diehard followers who hate spoilers, however oblique. Savvy and articulate, Archers devotees don't take radical changes to their favourite programme lying down. Whitburn hasn't actually leaked any particular storyline, but uttering words such as how developments in the 60th birthday special on January 2 will "shake Ambridge to the core" (SATTC) are enough to curdle the milk for many.

All we know, and she will go no further, is that the shocks will come from one storyline that's already running in the six-nights-a-week soap, and one scenario that's entirely new. Well, that got the twitterers tweeting and the listener forum frazzled with emotions ranging from furious agitation that the show may be about to enter into the sensationalist ratings-grabbing turf of TV soaps, to excited expectation, to downright bonkers speculation as to the nature of the surprises in store.

Some are fretting that Jolene, the depressed landlady of The Bull, who lost her beloved husband Sid a few months ago, will find Christmas and New Year just too much and do something desperate. Others are fearful about the impending birth of anorexic single parent Helen's longed-for IVF baby, with a mild side issue of whether her gay friend Ian-the-chef (who also longs for a child) moves on from matey decorating of the nursery to declaring his love for Helen and his need to be the child's dad. Where will that leave his gorgeous partner, farmer and king of the polytunnels Adam Macy?

The programme has been building up to some sort of cliff-hanger for little Phoebe, who is torn between love for her dad Roy Tucker and his wife lovely Hayley, and her new-found closeness to her natural mum, the brattish Kate Aldridge, recently returned from South Africa to study at Felpersham University. Will the little girl come to some harm while trying to run away to join Kate in Jo'burg for a New Year celebration? Ooh, let's not go there...

The as-yet-unknown event that will help to SATTC surely couldn't be the discovery of an al-Qaida cell hiding in one of the many outhouses at Bridge Farm. Or could the cataclysm that's to change Ambridge forever come from some terrible one-off disaster, such as the icy weather finally penetrating the village's famously mild microclimate, resulting in a giant snow plough crashing into Keeper's Cottage, taking out several members of the Grundy family at once? Few are allowed to visit Ambridge, a village of the mind for some, but a tangible place to others. Suffice to say it is somewhere in the environs of Birmingham, where the BBC studios also happen to be, cheek-by-jowl with the swanky Harvey Nichols. Those who believe The Archers is a reality show might wish to look away now, and resume reading further down the page...

I fully accept (through gritted teeth) that Ambridge is not real, but I'm one of those fans who can't bear to see photos of cast members. Pleasant looking though they all are, the actors do not at all represent the physical characteristics with which my imagination has endowed them.

So I look neither right nor left while visiting the studio, in case I catch a glimpse of Tim Bentinck and Felicity Finch (David and Ruth Archer) or Sunny Ormonde (who plays bon vivante Lillian Bellamy). Exotic though her name is, I doubt poor Sunny can possibly live up to my glamorous mental image of her alter ego.

Luckily the actors aren't in today, so Camilla Fisher, archivist extraordinaire and the "memory" of The Archers for the last 15 years, lets me have a snoop around the very place where every episode is recorded. Here's the full kitchen complete with cream-coloured Aga, cupboards full of pots and pans, and the kettle that's rarely off the boil. To think that Jill's famous cakes are cooked here...oh no, the Aga's not plugged in. There are two sinks, one ceramic and one stainless steel, depending on whose kitchen we're supposed to be in.

There's a carpeted area, a wooden-floored area and a tiled floor, and an extra wide but rather short staircase to nowhere, part of its width carpeted, part metal and part wooden, to fit in with different Ambridge interiors. A large wooden board is fitted with 16 different doorbells, those of the major characters in the show.

A sofa bed is unfolded as and when, so David and Ruth's bed-time chat sounds appropriately intimate, and slightly muffled by the bedding around them. A driving corner, with steering wheel and low-slung seats is used for the inside of a car. Various props used for sound effects are lying around – like the bucket of tangled cassette tape that's shuffled to make for a very realistic rustling of hay. An ironing board without its fabric cover is half unfolded then folded again to give the sound of a gate opening and closing. The sound technicians' desk next door plays in background music, farm machinery engines or animal sounds during recording.

It's difficult to believe that this is the hub of a world that encompasses a whole county, including a couple of market towns, various villages and hamlets, dozens of characters (okay, some of whom are heard about but never allowed to speak) and at times has travelled as far away as Costa Rica. This is the glorious wizardry of radio.

A pivotal cog in the wheel is Camilla Fisher, who sees every script prior to production and forward planning for storylines, which is done a year ahead. She checks for factual continuity, advises writers and producers, catalogues the births, deaths and marriages, CVs, recipes, exam passes, vets' bills and topical discussions of subjects like Pip's university choices and feelings about tuition fees.

She's the keeper of hundreds of thousands of pieces of data stretching back to the days when the programme was introduced as a means of broadcasting agricultural information from the government to farmers in the Midlands.

"Actors or writers email me most days to check on details they've forgotten", says Camilla. "It might just be something like they can't remember the sex of someone's dog, but that's the kind of thing listeners pick up on immediately if it's wrong."

The Archers is the most popular Radio 4 programme after Today, and although it was for a long time seen as a "female" programme, its male following is growing, says Joanna Toye, who has written scripts for the show for 30 years. Staff tend to stay with the programme for the long haul.

"Over six decades it has become like a social history of Britain. It doesn't get involved with specific news events - or rarely – but it reflects changes going on in society, such as the growth of same-sex 'marriage' or increasing numbers of people caring for a loved one with dementia."

Graham Seed, who has played the sweet, sunny but rather dim Nigel Pargetter for three decades, says he thinks the soap has lasted so long because listeners feel they are part of The Archers family and vice versa. And for an actor, typecasting isn't a problem posed by radio.

"I don't get recognised in the street, I get to play a charmingly witless character and be part of this amazingly talented group of people telling stories that mean a lot to people, and I have enough time to go and do stage or TV work. I feel very lucky".

Vanessa Whitburn thinks there are three major factors that contribute to the continuing success of The Archers. "Our listeners have often grown up with the programme and it reflects goings-on in their own lives; there is also a certain idyllic, fantasy element to it which people hold dear and I think fans appreciate that we work hard to maintain a balance between gentle stories, dramatic events and entertainment."

But how does she think listeners will react to the ructions caused by impending dramas that promise to shake Ambridge to its core?

"I think they're strong enough to take them. We do realise that balance is everything...and we don't take our audience for granted ".

We do realise that balance is everything...and we don't take our audience for granted.. ".

Over six decades it has become like a social history of Britain... it reflects changes going on in society...

Soap gives up its secrets...

The Archers editor Vanessa Whitburn leads a 10-strong production team and 11 writers as they plot the twists and turns of life in Ambridge.

Guest stars over the years have included John Peel, Sir Terry Wogan, Britt Ekland and Princess Margaret.

Julie Spencer, who plays Peggy Archer, is the longest serving cast member, first appearing in the pilot episode on May 29, 1950.

The theme tune to The Archers has been played more than 70,000 times in Britain since that first episode.

There are around 50 speaking characters in The Archers, but only five to seven appear in each episode.

Past scriptwriters for the show include novelists Susan Hill and Veronica Henry and historian Christopher Lee.

The Archers half-hour 60th Birthday Special will be broadcast at 7pm on Sunday, January 2. Vintage episodes can be heard during that day on BBC Radio 7.