Stop giving the game away with spoilers, you blithering twerps!

One of many good reasons never to go to the cinema — apart from all the slurping and munching around you, the eight-year-old kicking the back of your seat and the dazzle from dozens of accursed smartphones — is the movie trailer.

Modern trailers don’t just give you a taster of next week’s attraction — they ruin it.

Plot, characters, twists, climax, they give the lot away. If you’ve seen the trailer, you never need to pay to watch the film.

The opening collage of clips in Reported Missing (BBC1) made the same dreadful mistake, revealing the ending of what should have been a gripping documentary.

We’ve seen the same collection of quick-cut shots at the start of each episode, riffling across the screen. They haven’t altered. But if you’ve watched the whole series, by now some scenes will stand out — the ones you haven’t seen yet.

These included searchers in mountain rescue gear scrambling through woodlands, a confusion of bodies around a red stretcher, a cry of ‘I’ve just found him now’ and an old man’s gnarled hand reaching from under red blankets to squeeze a woman’s fingers.

Those images played no part in previous stories, so it was obvious what we could expect.

As soon as the case began in earnest and we learned that 82year-old Archie had gone missing from his Darlington home, there was no doubt about how this was going to end . . . in a wood, with rescuers and a red stretcher.

And so it turned out. We discovered the fingers belonged to the old fellow’s niece, but it wasn’t really worth waiting for that. A piece of inexplicably bad editing had spoiled the whole hour.

That’s a great shame because this detailed account of a police investigation was easily up to previous high standards.

All credit to Peter, son of the missing Archie, for retaining his sense of humour and allowing us to see every stage of the hunt — including the bit where officers decided Peter had probably murdered his dad and hidden the body under the loft insulation.

even without the benefit of the Beeb’s spoilers, most viewers must have seen Peter wasn’t lying about Archie’s disappearance. The inconsistencies in his story were simply due to exhaustion from worry. Meanwhile, the coppers were being a little too frank in front of the cameras.

One admitted that, after 30 years on the force, he was so cynical he trusted no one but his family. ‘And my colleagues,’ he added, unconvincingly.

With material like this, it’s all the more a pity that the tale was needlessly wrecked. Strangely enough, How To Live Mortgage Free (C4) made the same mistake, though to less ruinous effect. In the opening sequence of this show about unconventional, low-cost homes, we glimpsed a copper bathtub stowed beneath a kitchen unit.

Later, we met Katie, whose boyfriend Freddie was building a mobile home for them on a hay bale trailer. Her only complaint was that Freddie’s plans included a shower, but no bath.

Presenter Sarah Beeny looked horrified: ‘Showers are nasty wet things,’ she yelped. ‘Baths are the only way forward.’

At this point, the attentive viewer who had seen the opening sequence might have thought: ‘Hello . . . I can see where this is going.’

And, indeed, the big ‘surprise’ was that the show’s handyman had knocked up an elegant bath on wheels, hidden in the tiny kitchen.

The even bigger surprise was that everyone expected Katie to use it outdoors on the balcony. no one saw that twist coming.

SLOWBURN OF THE WEEK: A new episode of Better Call Saul arrives on online streaming service Netflix every week. For addicts of this Breaking Bad prequel, it’s a joy . . . if you don’t mind a plot that’s slower than a tortoise on Valium.