Parade's End: A series to challenge Downton

With Benedict Cumberbatch in the lead role and Tom Stoppard in charge of the script, the BBC's adaptation of Parade's End will threaten ITV's all-conquering drama. They talk to Gerard Gilbert

Benedict Cumberbatch and Rebecca Hall in Parade's End (BBC)

Benedict Cumberbatch is furiously scrolling through his iPhone, the actor trying to locate a quote that he believes summarises his character, Christopher Tietjens, in BBC2's upcoming period drama Parade's End. Ford Madox Ford's quartet of novels, written between 1924 and 1928, has been adapted for television by Sir Tom Stoppard.

"I've got every single script I'm sent on my mobile," says Cumberbatch distractedly, pausing briefly in order to shake hands. "There is this amazing moment in episode two when Valentine (his lover in the story) asks, 'Why do you hate your country?' and he says, 'I don't. I love every field, every hedgerow. I just hate what's been done to this country; it's been taken over by moneylenders.' And basically he goes on to define his version of Toryism, which is feudalism really."

All this is delivered in a torrent familiar to anyone who knows Cumberbatch and his restless, super-charged mind – although comparisons to his most famous creation, BBC1's Sherlock Holmes, are unwelcome. "Because I talk a lot, probably because I'm nervous, I get pinned into the same mania bracket," he says.

Parade's End follows Tietjens, "the last Tory", a brilliant government statistician from a wealthy Edwardian landowning family married to a flippant, adulterous socialite, Sylvia (Rebecca Hall). Despite public humiliation, he refuses to divorce her because of what he terms his "parade" – an outmoded code of ethics that is tested by the mass slaughter of the First World War, and then by Tietjens' growing love for a young suffragette, Valentine (played by Australian newcomer Adelaide Clemens). It's a journey, says Cumberbatch, from romanticism to modernism.

The five hour-long episodes are strikingly filmed by the director Susanna White (Bleak House, Generation Kill), with nods to such modernist art movements as Vorticism and Cubism. But by following the same late Edwardian aristocratic caste through the First World War and into the 1920s, could Parade's End be fairly dubbed "a thinking person's Downton Abbey"? "I guess that's a crude label for it," says Cumberbatch. "Not to denigrate what you're saying, but any comparisons are a danger." However, without naming names, he later says that Parade's End won't be "some crappy, easily digestible milk-chocolate on a Sunday evening… it's going to be hard work, but it will pay dividends if you stick with it".

Tom Stoppard, who last wrote for the BBC way back in 1979, began work on his adaptation four years ago, long before Downton Abbey seduced the world, and what Stoppard calls "the current festival of toffery". "I was well into the thing before I'd even heard of Downton Abbey and decided not to watch it," he says, before adding that "great minds sometimes think alike".

"I remembered a friend telling me about going to dinner in a stately home and saying to his host, 'Your butler is very impressive.' The host replied: 'Not really – he buys in his chutney.' I put that into Parade's End, and then somebody said to me that Maggie Smith says something like that in Downton Abbey (it was actually in Julian Fellowes's script for Robert Altman's Gosford Park – where Maggie Smith's character dismisses 'bought marmalade… how feeble'). Anyway, I called Julian Fellowes up and he said, 'Oh, just carry on, don't worry about it' – so I took it out and then put it back in. In the end, the things that are similar between these different dramas are much, much less significant than the things that are dissimilar."

Indeed, it's highly unlikely that the subtle moral ambiguities and complex historical metaphors of Parade's End will appeal to the mass audience that imbibes the unashamedly sudsy Downton Abbey. "It's more ambitious," agrees Stoppard, who spent 15 months on his script – having first read the books, he says, in the decidedly incongruous setting of Copacabana Beach in Rio. "It's one of the key modernist novels. This was the period when The Wasteland and Ulysses were published. It was never a huge popular success, but I met four or five people who said, 'Oh, you're doing Parade's End – it's my favourite novel.'

"I must say I absolutely loved the job," he continues. "Ford was writing at a time when he was interested in experimentation – he puts you inside people's heads and sometimes these people haven't got their heads straight and you have to find your way through the maze of their thoughts. I had a conversation just a few days ago about The Great Gatsby movies and about the novel. I personally think that The Great Gatsby is a great novel, but how do you put its greatness into a screenplay?"

Adaptations have been on Stoppard's mind recently, having simultaneously written the screenplay for the upcoming Anna Karenina movie, starring Keira Knightly. In fact, during our interview he takes a phone call from Joe Wright, Anna Karenina's director. "The projects had virtually simultaneous shooting schedules," says Stoppard. "If I get a call about Parade's End when I'm talking to Joe, I say: 'I'm terribly sorry, it's my mistress,' and if I'm talking to Susanna (White) and Joe calls, I say: 'I'm sorry Susanna, I have to talk to my mistress.' They both think they're married to me."

Stoppard and White had Cumberbatch in mind right from the start. This however was before Sherlock made his name international, and with half of Parade's End's £12-million budget coming from HBO, the Americans were doubtful. "To us he was well known," says Stoppard. "I'd seen Benedict playing roles at the Almeida and other places and I knew he was bloody good, but he wasn't a star by any means. Sherlock actually happened when we were putting it together, which helped a lot."

Stoppard's assiduous and almost fearful wooing of his leading actor began during a visit to the set of War Horse. "Tom kept on looking at me sideways and he said to me, 'You've had such a wonderful, extraordinary year Benedict,'" says Cumberbatch. "It was lovely but there was something slightly odd about the conversation and he confessed to me later was that it was agony for him because he wanted to offer me the role there and then.

"The weird thing is I couldn't get past certain things. Christopher is a big man and I was really distracted by that at first. I wanted him to be fatter and rounder; I was thinking of a young Gambon or – dare I say it – Matthew Macfadyen. I've said that before – he's going to punch me next time he sees me.

"I'm this willowy man worn to the bone by doing Frankenstein (at the National Theatre). And then with Sherlock, having to be whippet-thin again and eating rice cakes, and running and swimming a lot. I had to put on this fat suit and plumpers in my face [for Parade's End]. I wish we'd gone further with it, but they stopped me going the whole hog because they wanted a pin-up. He's got to be seen as sexually attractive or why would someone as beautiful as Valentine fall for him?"

In the end, Cumberbatch visualised himself into the role by way of the Mayor of London. "I saw him as Boris Johnson to start off with," he says. "A very intelligent but rather oafish buffoon."

Does the actor now yearn, I wonder, for a change from all these fiercely intelligent men he keeps playing? "I'd love to do a slacker comedy where I'm just getting stoned," he admits. In fact Parade's End, and the new series of Sherlock, which begins filming in January, could be the last we see of Cumberbatch in television roles.

Playing Khan, the obligatory British baddie in next year's new Star Trek movie, and co-starring with Brad Pitt in Steve McQueen's latest venture, Twelve Years a Slave, about an educated mixed-race 19th-century New Yorker (Chiwetel Ejiofor) who spends more than a decade on a Louisiana cotton plantation after being kidnapped, has whetted Cumberbatch's appetite for a larger canvas.

"I'm playing a really big game now," he says. "I'm going into studios to meet executives and heads of production and asking: 'What have you got on your slate?' and they say, 'This and this and this.' And you know there are five actors ahead of you who have first refusal, so there will be fallow periods now, but I can't afford another five months in the theatre or another big TV gig.

"I think it's time. I don't have any dependants. I'm interested in just playing the game a little bit, because it gives you a lot more choice. It gives you power and if you become indispensable to that machine it gives you a greater variety, which is what I always wanted. My career's always been about longevity – I've never wanted to be an adolescent flash in the pan. Brad Pitt, Clooney — they're in a really privileged position where they are the men who get film screen net [a share of box office receipts], and there are about five people in the world who can do that. They're great people to emulate as a business model."

'Parade's End' begins on Friday 24 August on BBC2