Inside the Abbey

(NICK BRIGGS)

It wasn't the kind of weather that you imagine for a visit to Downton Abbey – as played on television by Highclere Castle on the Berkshire-Hampshire border. This was no Edwardian-style summer's day, deep shadows on the manicured lawns and all that – instead, a bank of low pressure pushed squally rain up the M4 corridor. But then, the dark clouds had been gathering for the aristocratic Crawley family and their servants – and for the 13 million of us following their exploits – since the first series of the ITV drama ended in December with the Earl of Grantham (Hugh Bonneville) taking that telephone call with the news that Great Britain was at war with Germany.

Julian Fellowes' costume drama became the television phenomenon of last year. Downton Abbey has gone global, selling to more than 100 countries and, recently, securing three Emmy nominations. Fans include the Duke and Duchess of Cambridge and Joanna Lumley, who pestered Fellowes to write her a cameo.

After driving over a bridge across the busy A34 from Newbury to Southampton, you are suddenly in a different era – a secluded idyll with sheep grazing on Capability Brown parkland that probably contains more cedars of Lebanon than they have in Lebanon. The famous castellated turret makes itself known over the brow of a hillock. Such a magical effect for any fan of the series is only spoilt by the lorries, marquees and catering trucks that are clustered in front of the house. Filming is in progress.

I spot Bonneville on the gravel driveway with a parka over his Edwardian formal wear, trying to keep the rain out as he sips coffee from a polystyrene cup.

"We've just come out of the war and now we're facing Spanish flu," he explains, helpfully, before being whisked away to shoot a supper scene from the eighth and final episode (not counting a Christmas special) of the forthcoming series.

This is taking place in Highclere's state dining room(Highclere belongs to the Earl of Carnarvon, who has wisely gone racing for the day) in the panelled dining room. Seated around the table, waiting for the call to action while peering into plates of what looks like Brown Windsor soup, are Bonneville; Elizabeth McGovern (Lady Cora, the American heiress married to the Earl); Maggie Smith (Violet, Cora's mother-in-law from hell – the Dowager Duchess of Grantham); Penelope Wilton (Violet's sparring partner, Isobel Crawley); Michelle Dockery (Lady Mary); and Dan Stevens (Lady Mary's true love, Matthew Crawley).

In the new series, Downton has been turned into a convalescent home – the daughters of the house becoming lorry drivers, nurses and suchlike. But my quest, apart from having a snoop round, is less to give away plots from the second series than to pinpoint the appeal of the first. I was not an immediate fan – frankly, Downton Abbey seemed a bit clumsy for a viewer raised on the meticulous standards of BBC period drama. Hilariously unsubtle at times, in fact. The series grew on me – albeit never to the point of infatuation. "People find Downton Abbey relaxing," McGovern tells me. "My contemporary brain finds it very relaxing, looking at an age when everybody knows how to behave because the rules are very clear. In the world of Downton Abbey everybody knows what's expected of them."

Downton Abbey became a bit of a laughing stock last autumn when, in one shot, a television aerial was spotted. Other viewers claimed to notice a car from 1921, a modern street sign, someone playing "After You've Gone" on the piano – it was not written until 1918 – and double yellow lines in a scene set in a village street.

"There aren't any double yellow lines in Bampton [the Oxfordshire village that stands in for Downton," says the series producer, Nigel Marchant. The TV aerial existed, however. "You watch the show so many different times – and there's always something," he allows.

Fellowes, who is planning a "nit-pick of the week award" for the new series, hit back: "The real problem is with people who are insecure socially, and they think to show how smart they are by picking holes in the programme to promote their own poshness and to show that their knowledge is greater than your knowledge."

Dockery, who plays Lady Mary, believes that Downton Abbey has the advantage that, unlike most costume dramas, it is not based on a classic book. "So there's nothing to compare it to," she says.

Whatever its causes, the "Downton factor" is good for the ITV share price and healthy for local tourism. The number of coach parties visiting Highclere has quadrupled and un-official Downton tours have sprung up. Paparazzi have taken to hiding in the rhododendrons, seeking sneak snapshots of the cast. One tried to disguise himself by putting a fire warden sign on top of his car; another, in full camouflage army gear, was apparently flushed out by Lady Carnarvon.

Downton Abbey' returns to ITV1 in September