Doctor Thorne is ideal Sunday night period drama — froth peppered with darkness

I can see his point, though. He meant that it's not like Downton because it's a self-contained three episodes rather than six whole seasons. There's nothing sprawling or epic about Doctor Thorne, Fellowes' ITV adaptation of Anthony Trollope's 1858 novel.

And let's thank the TV gods for that — because Doctor Thorne's limited scope means it's sharper, more succinct and therefore more thrilling than Downton was, particularly in its later series.

But despite being only three parts, Doctor Thorne does share with Downton many of the things which made it such a huge hit. It's full of the most beautiful country houses, castles and corsets, with some brilliant characters and actors at its centre. Here, Rebecca Front and Tom Hollander are the leads in an exciting story of love, money and class divide.

But there is also darkness at its core, with the central romance overshadowed by a murderous secret known only by Doctor Thorne. Played by Rev's Tom Hollander, Thorne is a good man who has looked after his niece Mary (recent RADA graduate Stefanie Martini) all her life. She is in love with old friend Frank Gresham (another newcomer, Harry Richardson) but is resisting his advances because, as a penniless outsider, she deems herself unworthy of him. And his mother Arabella, the brilliant Rebecca Front, wholeheartedly agrees, desperate that her son "marries money" rather than Mary.

Front plays the matriarch wonderfully — comic in her obsession with fortune but without being a villainous caricature. Her performance makes you see why, in Lady Arabella's tiny world, her son marrying well is so crucial. "Being close at 12 is very different to being close at 20" she remarks, with great concern, about her son's enduring friendship with Mary.

Tom Hollander is also great, and looked rather embarrassed by the deluge of praise he received at the launch. Fellowes told the audience that Hollander has the rare talent of being "charismatically nice" on-screen — moral without being boring. At that, Hollander reddened like a true 19th century gent.

Asked how on earth the cast made sure their posture and body language were true to the era, Hollander revealed that Fellowes policed the cast on set. He said that while filming Gosford Park 20 years ago, Fellowes told him, sharply, to get his hands out of his pockets and that, two decades later, the writer said exactly the same thing to newbie Richardson while filming Doctor Thorne. Clearly standards haven't slipped one bit.

The two young leads are impressive, especially Martini who is charming while inspiring real sympathy as a young woman at the mercy of a brutal class system. Discovering something shocking about her past in the first episode, she resigns herself to a fate without true love. Mad Men's Alison Brie, Game of Throne's Ian McShane and Wallander's Richard McCable are also brilliant.

The lightest, funniest relief is provided by Fortitude's Phoebe Nicholls as the scheming Countess De Courcy. She is shamelessly obsessed with her nephew Frank marrying a rich woman, with plenty of outrageous lines which made the audience laugh out loud during the preview screening.

Fellowes has created a period drama that feels classy, well-acted and sharp. Ideal Sunday night fun, its engrossing central storyline is froth peppered with darkness. And if this one goes down well, there are 46 more Trollope books to draw from...

Maybe it really is the new Downton after all?

Doctor Thorne is on Sunday 6th March at 9pm on ITV