ON encountering Murder Island (Channel 4, Tuesday), a whodunnit/game show with a £50k prize, any half decent detective’s first move would be to ask who came up with such a crass idea.

Then again, when it comes to fictional crime, the ship of good taste sailed long ago. From Cluedo to game show, it was only a matter of time. But still, really?

If you could put such reservations to one side, Murder Island had its moments, most of them courtesy of the utter cluelessness of the amateur sleuths trying to find out who had killed eco-warrior Charly on the fictional island of Hirsa (Gigha more than ready for her close up). Among their blunders was traipsing through blood at the crime scene.

The days leading up to the killing were seen in flashback. It was like watching an old Crimewatch, complete with the same iffy standards of acting. The story, by Ian Rankin no less, was not much better.

Thank Taggart, then, for Dot and Rox, two Londoners who were not so much Cagney and Lacey as Laurel and Hardy. One of them had brought a picture of their dad as a motivational tool after he predicted they would be useless. No comment, as they say in police interviews.

It is not easy to make a documentary that is joyful and heartbreaking at the same time, but Dementia and Us (BBC2, Tuesday) made the task seem like a stroll through autumn leaves.

The concept was straightforward. Choose four people with dementia and their families and keep in touch over two years to see how the condition progresses.

This was not an exploration of the condition by someone in a lab coat. This was straight from the front line reportage involving wet sheets and melted kettles.

“It’s not the life we had planned for each other,” said Christine, carer to her husband, Gilly. “I want people to see us being positive but I also want people to see the pain.”

We met Chris, diagnosed ten years ago at the age of 33 with early onset dementia; Marion, who called herself “the gobby one”; and Clover, a former nurse now looked after by her daughter. The aim was to show the range of the condition. In every case, however, the prognosis was the same. Life was going to get harder, and so it proved.

Filmmakers Paul Myles and Zoe Jewell had extraordinary access (in one instance the cameras were present when someone received test results), but they were always respectful and never intrusive.

Ridley Road (BBC1, Sunday) had more shades than a paint card. Adapted from the novel by Jo Bloom, it was the tale of Vivien, who leaves her family home and fiance in dreary old Manchester for the groovy streets of London just as the Sixties are starting to swing.

Vivien (Agnes O’Casey) is in search of her true love, who turns out be part of a Jewish band of brothers and sisters battling the rising tide of British fascism.

The scenes featuring the far right thugs were chilling, but the next minute the action switched to the Soho hairdressers where Vivian had found a job. “I used a whole can of lacquer,” cackled saucy manageress Barbara (Tamzin Outhwaite, EastEnders), admiring a recent “do”. “You could throw rocks at it, it won’t budge!”

The all over the shop tone would have been more of a problem if the cast was not so top drawer. Eddie Marsan and Tracy Ann-Oberman on a Sunday evening? I won’t say no.

It is always heartening to see a newbie finding their feet on the slippery slopes of television fame. Welcome, then, to the presenter of Iceland with Alexander Armstrong (Channel 5, Wednesday). Oh, hang on, that Alexander Armstrong, the one who is on every TV set in Britain, every day, like a layer of dust? The very same, but this is his first major gig with Channel 5 so wind your neck in.

Everything with Armstrong was either brilliant, blissful, or otherwise marvellous as he dived into the attractions, including a geothermal lagoon where drinks were served (“It’s a bit like a pub, in a bath”). While his relentless cheer became exhausting after a while, and I cannot imagine how they are going to string this out for three hour long episodes, he won me over eventually.

Mortimer and Whitehouse: Gone Fishing (BBC2, Sunday) reached the end of its current run with the boys on the River Severn hoping to catch zander (no idea).

The ending was subdued compared to previous finales. That better not be a sign the show is approaching its sunset. They can’t give up just yet, particularly now Ted the talking dog (courtesy of Whitehouse) has arrived.

As I watched the credits roll to the sound of water lapping and ducks quacking I saw the series director’s name was Rob Gill. If that’s not a sign from God to keep going, I’m a zander.