First Night: Titanic, ITV1

Last night certainly wasn't the first time ITV has spent a fortune inducing a sinking feeling in the television audience, but at least this time it's what it actually planned to do. Four times, in fact, since Julian Fellowes' latest television drama, Titanic, looks at the disaster from a different perspective in each episode, allowing the ship to sink a little lower in the water each time.

Unprepared viewers may have been startled to find that we seemed to be barely out of Southampton in screen time before the iceberg struck.

They won't have been very surprised, I think, to discover that Fellowes' essential preoccupation remains the same as Downton Abbey here – the fine gradations of social distinction.

Fellowes is a self-styled Titanorak, fascinated by the sinking and determined here to do justice to the historical record. There are times when this puts the naturalism of his dialogue under strain. "But there are davits for 32 lifeboats ... why on earth haven't we used them," says the ship's designer as he chats casually with the chairman of the White Star Line, Bruce Ismay.

"Because there is no need," Ismay replies. "The law stipulates 16 lifeboats and that is what we have... I will not have the promenade deck ruined or the ladies terrified."

For the most part, though, this is Fellowes as we know him – a combination of punctilious details of etiquette and flagrantly implausible breaches of it. At one moment, a parvenu character is being ticked off for not knowing that it isn't the done thing to change for dinner on one's first night at sea, and at the next, a saucy Italian steward is winking at Lady Georgiana in the first-class dining room.

Lady Georgiana is here, ironically, to keep her out of trouble – her anxious parents Lord and Lady Manton having decided that a transatlantic trip is the best cure for her alarming Suffragette tendencies. Also on board are real-life figures – including the film star Dorothy Gibson, Second Officer Lightoller, a Guggenheim and some Astors – as well as the fictional characters, who allow Fellowes a little more latitude in his plotting. Naturally, once the iceberg has hit, the class system is more than a match for any fatuous notion that everybody is, literally, in the same boat.

As a steward slams the grilles on the third-class passengers, first-class ladies bicker about the seating arrangements in the lifeboats. And, because viewers will have to wait for next week for the more interesting overlaps to reveal themselves, it looks for now like a conventional telling of the story rather than a revelatory one. It has miraculously speedy romances, villainous plutocrats and relishable moments of Edwardian stiff upper lip. "First I will change into something more gentlemanly," declares Benjamin Guggenheim calmly, as the saloon starts to tilt, "then we will wait upon events." A fine moment, but as any Titanorak will know, life supplied that scene, not Mr Fellowes. We still have to see whether he can invent anything as good.