Every now and then, a costume drama comes along that’s so daringly unconventional as to make us re-examine our whole idea of what the form can achieve. ITV’s Doctor Thorne, though, isn’t one of them. Instead, Julian Fellowes’s adaptation of Anthony Trollope observes the usual rules with almost pathological fidelity. Extras dance gamely in ballrooms, scheming matriarchs stand in the way of sweet young lovers and characters express deep fury with the words, ‘Good day to you, madam.’ In the first scene, we even had a handy refresher on the genre’s use of hats as a social signifier. (Basically, toppers for the toffs, peaks for the proles.)

The title role is played by Tom Hollander, now in competition against himself on Sunday evenings, where his slightly odd turn as a gay henchman continues in BBC1’s The Night Manager. For ITV, he’s returned to more Rev-like form, with Thorne a decent bloke trying to do his best in a world far less nice than he is. He has, for example, acted as a father to the toothsome Mary, the illegitimate daughter of his late brother — a man attacked and accidently killed by a peak-capped prole 20 years before. Not only that, but he’s become a sort of friend and financial adviser to the prole in question, Roger Scatcherd. Having served ten years for manslaughter, Scatcherd is now a wealthy railway magnate, but still enough of a ruffian to spend his days swigging from a brandy bottle while cackling.

In his spare time, Thorne is also trying to help his neighbours, the Greshams, whose large estate is now mostly in hock to Scatcherd and who therefore need their children to marry money. Unfortunately, their son and heir Frank is in love with Mary — a woman whose fondest wish is to be able to afford a bonnet.

As befits its commitment to costume-drama tradition, Doctor Thorne brings us a reliable selection of frock-coated and corsetted British thesps. Along with Hollander, who’s fine without ever appearing to be at full stretch, there’s Rebecca Front doing a neat job of suggesting the financial anxiety beneath Lady Gresham’s snobbery — and Ian McShane clearly enjoying the chance to do some serious shouting as Scatcherd. In the tricky role of the young would-be lovers, Harry Richardson and Stefanie Martini seem suitably superior to the money-grabbers around them and yet not too sickly. I may not be the first person to spot this, but Julian Fellowes does have an interest in class — so the programme is good, too, at revealing the many social gradations lying behind the action.

In other words, Doctor Thorne already looks likely to succeed in what seems to be its primary aim — by no means an unworthy one — of providing some pleasantly undemanding viewing on a Sunday night. Nonetheless, and maybe (but only maybe) because it comes so soon after War and Peace, it feels solidly competent rather than inspired.

Still, if it’s less controlled drama you’re after, there’s always The Aliens (E4, Tuesday), which turns out to be Doctor Thorne’s spookily exact opposite: messy to the point of bonkers, but also made with undeniable oomph.

The set-up is that aliens crash-landed on earth (or maybe just in Britain) 40 years ago — and, despite looking human and speaking English, are regarded with such suspicion that they’ve never been allowed to take their place alongside the rest of us. Some do perform menial tasks in the outside world, but every night they’re locked back into their own walled enclave, patrolled by border guards.

At this point, shrewder viewers might already have realised that one element of the show is an allegory about immigration. Luckily, on Tuesday that soon disappeared into the background to be replaced by a winningly unhinged plot based on the fact that, when burned in a pipe, the aliens’ hair is a powerful recreational drug. This has, in turn, led to gang wars within the alien community — into which a border guard called Lewis (Michael Socha, so great in the various This Is England series) is drawn when one of the gangs kidnaps his drug-dealing sister. Oh, yes, and Lewis has discovered that he is himself half-alien, and he’s not too pleased about it. He’s also formed an alliance with a gay alien who fancies him.

The result is a kind of mildly sci-fi version of BBC2’s award-winning The Wrong Mans with two unlikely heroes, completely out of their depth, finding themselves at the centre of an increasingly twisting storyline that involves lots of baddies trying to kill them. True, The Aliens doesn’t have the same level of ingenuity. Even so, it does manage to be a comedy thriller that’s both quite funny and quite thrilling — which definitely qualifies it as well worth a watch.