Best TV on today - Bank Holiday Monday 2nd January 2017

It has a great cast, too, possibly better than the material deserves. There’s Alex Jennings as Lord Hamilton, The Halcyon’s owner, a man with a wandering eye, indeed a wandering everything (he’s squiring brassy floozy Miss Lambert, played by Charity Wakefield); Olivia Williams as his sad, humiliated, brittle wife; and Steven Mackintosh as the hotel manager, the man who keeps the secrets. Meet the cast of The Halcyon and find out where you've seen them before with our handy guide.

Great British Railway Journeys, 6.30pm, BBC2

“I must have left King’s Cross station a thousand times before but never with these crowds… and never with this style,” says Michael Portillo, just a little smugly, as he settles into his seat on the restored Flying Scotsman.

On its early trips the steam locomotive stopped at York for a quick lunch break, and an even quicker comfort break at Newcastle. Not so on this journey (Portillo’s served lunch and dinner on board in between chatting to fellow passengers) although the train’s forced to stop to refill with water and to clear the track of reckless steam enthusiasts. It’s a glorious, romantic reminder of a bygone era.

Silent Witness, 9pm, BBC1

After 20 series it’s time the Silent Witness lab had a security guard on its front doors simply to stop distraught members of the public from bursting in to demand their relatives’ bodies.

In the first of a two-part story a young woman insists that a severed finger Nikki is examining belongs to her mum. Quite how she knew her missing parent’s digit is in the Lyell Centre is inexplicable - but that’s Silent Witness for you. The ad hoc amputation is merely the very tip of a hideous iceberg of people smuggling involving a merciless gang of trafficking extortionists who take everything from Syrian refugees desperate for a better, safer life.

An Island Parish, 8.30pm, BBC2

For its 12th series, the BBC2 stalwart awards itself and us a winter getaway and takes us to the island of Anguilla in the Caribbean. “This paradise is extremely fragile,” rumbles sonorous Bishop Errol Brooks, and though he doesn’t enlarge on why we gather that the island, though idyllic, has few natural resources – water is scarce and the soil poor – while tourism puts a strain on its systems.

Among the bishop’s flock we meet Anna (originally from Cornwall), who looks after the gardens at one of several luxury resort hotels. When her manicured grass goes yellow in the heat, we see how she keeps up appearances – by spraying it with green paint.

!mpossible, 2.10pm, BBC1

Rick Edwards hosts a decent new spin on multiple-choice quizzing. As well as a right and wrong answer, there’s an impossible one. If any of the 30 contestants give it, they’re instantly eliminated. So for instance, answering “Rising Damp” to a question that begins “Which BBC1 sitcom…” would be death, because it wasn’t a BBC1 sitcom.

There are some clever variations on that theme as the competition progresses towards a daily cash prize and a tilt at the jackpot, which is £10,000, all in pound coins that are apparently primed to cascade into the studio. That might happen soon if this first episode is any guide: most RT readers will get the final question right straight away.

The Undateables, 9pm, Channel 4

Not much could warm a cold January heart more than the return of this dating series, in which the hopefuls all have a condition that makes them doubt they can ever find love. What we see is that their concerns about rejection and incompatibility are the same as anyone who opens themselves up to appraisal by a stranger – although their bravery in letting a million extra strangers at home watch them is greater than your average dating show participant.

In this episode we meet Sam, who has Asperger’s; Ian, whose diminishing vision means he wants to meet the love of his life quickly; and Kate, who says, “Funny is kind of important – I like guys that make me laugh”. Kate insists on this despite living with cataplexy: if she laughs too hard, she collapses.

First Dates Hotel, 10pm, Channel 4

Blind dates are nightmarish enough, but in this First Dates spin-off, these singletons’ suitcases must be rammed with valium. Not only do they have to travel to rural France, they then stay in the same hotel and decide whether to have another date the next day.

French maître d' Fred is in his element, leaping around with baguettes, and sommelier Xavier says wonderfully French things like, “fine wine is a little bit like to be in love". Fashion model Kelly is searching for a man who'll pass muster with her dad, while street cleaner Bruce has been widowed for seven years and is determined to live life to the full and personal trainer Joey wants to find his first-ever boyfriend - who must have sticky-out ears.

Britain's Ancient Capital: Secrets of Orkney, 9pm, BBC2

If you think of Stone Age Britain, your first instinct would probably be to consider the area around Stonehenge as being at the heart of our neolithic life. But recent work being done on a hugely important site at the Ness of Brodgar in Orkney is making historians think again. And in a multidisciplinary new series, BBC2 is sending Neil Oliver, Chris Packham and a veritable passel of archaeologists and engineers over the stormy waters of the Pentland Firth to explore and tell us more.

From the DNA of voles to sea stacks via sophisticated stone monuments – and an unexpected use of seaweed – we’re getting an entirely fresh picture of the ancient Orcadians and how they created a culture that spread to the rest of Britain.