The world may be going to hell in a handcart but some things remain reassuringly unchanged: Julian Fellowes period dramas about feisty dowager duchesses, social climbing and snobbery, say. I like and admire Fellowes so I don’t want him to take this the wrong way. But when I say that his new series Belgravia (ITV) borrows from the same template he employed so successfully withDownton Abbey, and before that Gosford Park, and also in that series set on the Titanic that didn’t do quite so well, I’m not trying to suggest he’s a one-trick pony. More that he’s a canny chap who understands his market, has found the perfect formula and is damned if he’s not going to milk it for all it’s worth.

So, for example, in Belgravia — cunningly differentiated from Downton by the fact that it’s set in 1840s London rather than early 20th-century Berkshire — we meet an aristocratic battleaxe who entertainingly speaks her mind, suffers no fools and rails against the offensively newfangled ways of the times. Only this time, she’s played not by Dame Maggie Smith but by Dame Harriet Walter (whom perhaps either Fellowes or the casting director saw stealing the show as Logan Roy’s monstrous English first wife in Succession). And instead of electric lighting, the innovation that has invited her outrage is afternoon tea: ‘What is this newfangled tea?’

Both series also open with a big historical event — one so famous that even the all-important American audience is likely to be vaguely familiar with it. With Downton, it was the Titanic. With Belgravia, it’s the Duchess of Richmond’s ball on the eve of Waterloo. Both events have the added advantage of enabling key characters to die suddenly; or, perhaps, to appear to have died and then emerge back from the dead at unexpected moments.

Our heroes on this occasion are a bit more downmarket than the Earl and Countess of Grantham. James Trenchard (Philip Glenister) is a market trader made good. By supplying victuals to Wellington’s forces in the run-up to Waterloo (so efficiently that he is known as the ‘Magician’) he has made his first fortune, which he has then consolidated by becoming project manager for the builder Thomas Cubitt.

At this point, the script cannot resist serving up a fat dollop of Wikipedia. Lady Brockenhurst: ‘The great Thomas Cubitt? I assume he was no longer a ship’s carpenter at that time?’ Anne Trenchard: ‘You’re right. He started as a carpenter… He devised a new method for building and took in employ all the different trades involved — bricklayers, plasterers — so the people he worked for had only to give the commission. He and his brother saw to everything.’ Well, that’s one way of serving up the key info, I suppose, though you do wish it had been a bit less clunky. As you also do when Lady Brockenhurst describes Belgravia as ‘this spangled city for the rich where we all live’(!).

Being self-made, Trenchard is naturally required to be looked down upon by most of the upper-class characters. The script does lay this on with a trowel, too, rather. In the early scenes Trenchard’s wife Anne (Tamsin Greig) expresses to her daughter her anxiety about their invitation to the Duchess of Richmond’s ball in Brussels. Daughter Sophia: ‘You mean that by the normal rules we are not acceptable as company for the Duchess’s friends?’ Mother: ‘That is exactly what I mean and you know it to be true.’ People telling each other stuff they already well know? Hmm.

But I’m being catty. There are decreasingly few of us these days so socially attuned that we really notice and care if, say, a baron called Lord Bonkers is misdescribed in a newspaper as Lord John Bonkers (which should only be used as a courtesy title if he’s a younger son of a Duke or a Marquess or an Earl). The vast bulk of the market for Belgravia — and I’m trying hard not to be snobbish here — needs every last detail of social nuance spelled out with all the subtlety of a thwacking on the head with a croquet mallet. I’m sure, given the option, Fellowes would have much preferred writing a snob series where only U people would pick up on all the nuances. But it wouldn’t make any money.

That’s why, at this stage, I’m giving Belgravia the benefit of the doubt. Fellowes is good with his plots and there’s a nice one emerging — spoiler alert — involving the love child of Sophia and an unsuitable toff, quite redolent of Thackeray’s Vanity Fair. There’s also lots of promising below-stairs action, with the butler Turton (Paul Ritter, who’ll be fine once we’ve stopped noticing that he was the husband of Tamsin Greig’s Jackie in Friday Night Dinner) heading the household staff, who, I’m sure, won’t miss any opportunities at their communal dinners to explain any more social nuances we may have missed.

No, all right. It’s probably not going to be great art. But it is going to be great — and old school: none of that anachronistic diversity-casting nonsense — Sunday-night family viewing, and now we need this stuff perhaps more than ever!