Michael Portillo has barely been off a train since leaving politics, taking journeys blending scenery and history: it must be a relief receiving plaudits for edutainment instead of the abuse habitually heaped on politicians.

Sara Lund and Saga Norén have a lot to answer for. Their adventures in the murk of murder as they grapple with their own dysfunctional psychology entranced audiences who don’t speak a scrap of Danish or Swedish. The search has since gone on for other gripping instances of Nordic noir. How long can it be before we accept that The Killing and The Bridge both had ingredients that aren’t easily reassembled?

What did the Romans do for us? On the evidence of new drama Britannia, they pillaged, murdered and tortured, but also found themselves mesmerised by the psychedelic Druid magic that hovered over our ancient land like fairy dust.

The new import is the latest procedural from Scandinavia, this time focusing on Stockholm’s biker gangs. The first episode aired Tuesday night, with the rest of the series available on All4 now.

Henry VIII had a troubled marital history and Charles I lost his head, but both have also gone down in history as original, innovative and obsessive collectors of art, founders in different ways of what is now one of the world’s greatest accumulations in all media.

Accepted wisdom seemed to be that in the animal world rats and cockroaches were the most adaptable and the most widely geographically distributed, followed by those pesky humans. But think again: the premise in this new three-part series is that the big cats have also done a terrific job of spreading worldwide, each a different species within the genus.

“I’m black – I need to find out how black people live.” So reasoned Kiri, sitting in the back seat of the car driven by her social services case worker. She was on the way from her prospective adopters, a white middle-class couple who already had a teenage son, to pay a first unsupervised visit to her Nigerian-born grandparents. Kiri (Felicia Mukasa, pictured below) was mature beyond her years, open-minded and well-spoken, while her case worker Miriam (Sarah Lancashire) brimmed with mumsy good cheer and sensible advice.

Fans of Luther will be familiar with writer Neil Cross’s fondness for hideous violence, shocking plot-twists and macabre humour, as well as characterful London locations, and happily they’re all present and correct in this new sci-fi thriller.

You know where you are with Kay Mellor. Somewhere in the north, among a group of people brought together by pregnancy or prison, weight or, as in the case of the recent Love, Lies and Records, work. With Girlfriends (ITV), the common denominator is encroaching age. The drama's three protagonists are all knocking on a bit and wondering if life can possibly be so resoundingly over.

It’s not the first time that James Norton has kicked off BBC One’s New Year primetime celebrations in Russian style. Two years ago, he was costumed up as the courageous Prince Andrei, in illustrious ensemble company for Andrew Davies and Tom Harper’s War and Peace.