Sometimes, just sometimes, dramas have to do more than simply suggest brutality.  I don’t mean with endless, loving close-ups of a woman being tortured in a dungeon in a Silent Witness crime-of-the-week. I mean a depiction of a savage act that leaves no doubt that its consequences will be bloody and far-reaching. If a writer is going to lead us down the darkest of paths, we have to be convinced it’s right that we follow. It has to be worth the trip.

I try to remember this when a scene from the first episode of Good Cop returns to me, unbidden. I wish it didn’t, but there you go, it’s left a stain on me that can’t be rubbed away. It was a pivotal moment, the catalyst for everything that followed: a young police officer, John Paul Rocksavage, and his partner are lured to a house.

It’s an ambush, a revenge attack for a previous incident when Rocksavage (Warren Brown) confronted a thug who was harassing a young waitress in a restaurant. Rocksavage’s partner is made vulnerable when he’s deliberately isolated inside the house, and Rocksavage can do nothing but look on in despair as his colleague and friend is subjected to a well-planned and murderous beating.

This was a chilling, unforgettable piece of television, broadcast on BBC1 weeks before the fatal shootings of two police officers in Manchester. (The final episode of Good Cop was pulled from its original slot and is being aired this Saturday.) It left me shocked and upset, and has sat like a boulder on my brain ever since. I can’t dislodge it. But it was a piece of TV drama violence with a purpose. It made sense of everything that followed when Rocksavage took bloody revenge in what was an unusual, thoughtful piece of fiction that asked a lot of its viewers, confronting them with the question “Is it ever all right for a good man to do bad things for the right reasons?”

So it is a good thing that I remain haunted by that sustained, all-too-realistic looking beating. That’s the purpose of the very best television drama: to make me feel uncomfortable, to make me question my reactions.

And now we turn to the perfunctory new thriller Hunted (tonight at 9:00pm on BBC1) from the Spooks people. In the first episode of Hunted, where Melissa George plays a private security operative who suspects one of her colleagues is trying to kill her, there’s a murder. I can’t bear to go into details, but it involves a helpless victim’s eyeball, and a syringe. You can fill in the gaps.

I can’t forget that either, but for all the wrong reasons. It was a classic gross-out scene, a piece of violent flummery smeared on to a pointlessly complex plot for the emptiest of reasons - dramatic effect. I can almost imagine the script and the line “Put a horrible bit in here”. Hunted seems very proud of it, because it’s even repeated in the “Previously on Hunted” catch-up at the start of this week’s second episode.

A half-decent script wouldn’t need these hollow shock moments; there is nothing wrong with a shock moment if you have a good script (see Good Cop) but, if you don’t, it’s just cynical manipulation. There’s nothing thought-provoking about "the eyeball incident". It doesn’t make you consider anything deeper than “Dear god, that’s just horrible and I feel sick.”

In this week’s episode, there’s a torture scene where a man is tied to a chair and beaten in the face with coils of heavy chains. At this point, you might find that The Choir: Sing While You Work over on BBC2 provides the perfect refuge. 

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Hunted is on tonight at 9:00pm on BBC1.

Catch the final episode of Good Cop this Saturday at 10:30pm on BBC1.