Why does EVERY canal boat on telly have a serial killer in tow?

We used to love clowns. The silly men in the red noses and oversized shoes were the best thing about Bank Holiday circuses on telly.

But these days, if you see a clown on the box, he’ll be robbing a bank or torturing victims in a dank basement. His white-caked face and bald wig have become visual shorthand for an especially gruesome sadism. Our terror of clowns even has a name — coulrophobia.

A similar, irrational fear of narrowboats seems to be creeping into TV thrillers. These floating caravans ought to be the stuff of sunny memories, of Mr Toad or Rosie And Jim.

But when you see a canal barge in a murder mystery now, you can be certain a suspected serial killer will be lurking inside.

Off the top of my head, I can think of ‘houseboats of horror’ in Happy Valley, Luther and C4’s Belgian gore-fest 13 Commandments.

So it was no surprise that when police raided a narrowboat in Silent Witness (BBC1), they found a shifty individual with a serrated knife dangling from the ceiling by a lanyard.

Dr Nikki (emilia Fox) and the forensics experts at Rent-A-Pathologist Ltd quickly spotted that it was just the type of blade being used in a spate of murders of up to a really raunchy gag about a neck brace.

Catastrophe is pitiless about showing parents Sharon and Rob at their worst. They hooked up for a one-night stand in 2015 and now, while their friends have divorced and their careers have disintegrated, they’re married with two pre-schoolers.

Rob (a recovering alcoholic in real life) is wearing that brace because he crashed his car while blotto on vodka. Sharon is dealing with this by shoplifting and stalking her own husband.

Her character has always been the tougher, sassier of the two, but don’t make the mistake of thinking that she can cope with everything.

We saw her at her most vulnerable — not when being lectured by a store security guard, but when she was too scared to order a group of teenagers off the swings in her local park so her children could play.

Former Coronation Street star Julie Hesmondhalgh had a cameo as an attention-seeking fantasist who claims she was injured in Rob’s car smash. She once got so drunk herself, she says, that she burned the house down and killed her husband.

Rob and Sharon aren’t interested: they’re too busy bickering about whose death, his or hers, would traumatise their children most deeply.

Told you this sitcom has no time for good taste.