Lord Julian Fellowes is seated at a table with an immaculate and rather large three-tiered cream cake in front of him, scattered with fresh strawberries and cloaked under a tall glass cloche.
“Is it a decoration or is it supposed to be eaten?” he muses.
It turns out he did not order the cake in the glamorous London hotel we are seated in, but somehow it has appeared in front of him, as sumptuous, delicious and decadent as his most successful creation.
That creation is, of course, the confection that is Downton Abbey, an opulent period drama about the Crawley family, their majestic home of the title, and the staff below stairs who keep it all running.
It ran for six series on ITV, concluding with a Christmas special in 2015. No sooner had the credits rolled than fans began clamouring for more, ideally on the big screen.
Now that wish has finally come true, with all the original cast, including Dame Maggie Smith, Michelle Dockery, Hugh Bonneville and Joanne Froggatt, and new additions including Imelda Staunton and Tuppence Middleton.
“I didn’t really believe there would be a film, to be perfectly honest,” 70-year-old Fellowes admits, “because I didn’t see it as inevitable.
“I was a big fan of Mad Men, I was a big fan of The West Wing, I was a big fan of The Good Wife – there were no films of any of those.
“So I didn’t see that just because it had been a big success as a series that a film was inevitable.
“But in the end the rumbling grew louder and finally it seemed there would be and then we had to get on and think what it was going to be about.”
What he settled on was a royal visit from King George V and Queen Mary, which would send all residents of Downton into a tailspin.
“We wanted a central story that would involve everyone,” he says.
“There are lots of central stories that would have involved everyone but most of them are negative, most of them are epidemics and fires and disasters and I didn’t really want that. I wanted a positive central thing that would nevertheless involve everyone.
“Even if they were anti- it, they would have a reaction to it.”
He stumbled on the idea of a royal visit while reading Black Diamonds, a book about the Fitzwilliam family in Yorkshire.
“I was reading it and I thought, ‘Ooh, perhaps this is the answer – a tour of the county and they come to Downton for a night.’”
The plotline is sure to go down a storm not only with fans of Downton and the royals at home, but also in the US, where the show has been a resounding triumph and has been showered with awards.
Its success there reflects that of Fellowes, who has always found his reception warmer on the other side of the pond than he has on home shores.
“America has been very good to me, there is no question about that,” he agrees.
“I was an unfashionable type when I started writing and it’s no accident that it was an American, in the person of Robert Altman (the director who roped him in to write Gosford Park), that put me on the map because that wouldn’t have happened to me with the establishment in showbiz being what it is here.
“After I had won an Oscar (for that very screenplay), to a degree they were forced to reckon with me, but only to a degree. I was not what they wanted.
“And America has always been encouraging and welcoming and has – to say taken me seriously sounds a bit petulant, but nevertheless – given me a kind of weight that the English are very reluctant to do, so obviously I am very grateful to America’s interest.
“When I won the Oscar I said, ‘God bless America’, and I meant it.”
He’s written so many wildly successful and popular things, among them the TV adaptations of Little Lord Fauntleroy and The Prince And The Pauper, and films such as The Young Victoria andVanity Fair and Separate Lies, which he also directed, that it is perhaps surprising he felt he was not welcomed at home.
“I wasn’t left wing. There is a kind of donnée (assumption) you belong to the soft left if you are going to be taken seriously, culturally. The idea that you could be talented and not soft left is a contradiction in terms.
“It was that more than anything else,” he says.
“I don’t think my background was right,” he continues. (Fellowes was born in Cairo, Egypt, the youngest son of diplomat Peregrine Edward Launcelot Fellowes, and started out as an actor).
“And I had defined my type as an actor and they weren’t particularly prepared to reassess that in the light of my different career.
“But all of this sounds a bit as if I’m complaining. I’m not complaining, that is the way it worked for me and in the end I got the lucky break from somewhere else and as a result I have been very fortunate over the years and I had the chance to do lots of stuff, here as well as in America.
“To a degree I had the last laugh, but I think the Americans were very open to what I could do and I am very grateful to them for it.”
His upcoming projects are: a Netflix series about the origins of modern football, exploring the class divide facing enthusiasts who created the beautiful game; an adaptation of his novel Belgravia, about posh Londoners in the 19th century, and The Gilded Age, about the rise of new money in 1880s New York, which will feature Downton’s Dowager Countess of Grantham as a younger woman.
But he denies everything he writes is about class.
“School Of Rock has been a big hit for me and that is not about class. My own favourite piece of my own work, if you can say that, is a film I wrote and directed called Separate Lies, and that is not about class either.
“But these jobs keep coming for me. I am interested in class, I don’t want to deny it.
“I do find it interesting that even today the class you are born into has a very shaping effect on your subsequent life.”
Downton Abbey is released in UK cinemas today