Last night's viewing - Confessions of an Undercover Cop, Channel 4; Art of America, BBC4

What I was waiting for in Confessions of an Undercover Cop was for someone to ask about the tattoos. These days, Mark Kennedy, ex-policeman and ex-husband, has a lot of them – full-sleeve affairs complete with leering skulls and elaborate patterning. But in some of the pictures of him as Mark Stone, ex-environmental activist, ex-lover and ex-alias, you couldn't see them. I'm guessing, too, that he didn't turn up at Hendon Police Collge sporting tribal markings. So when exactly did he get the body art and what did it represent? Had he acquired them during his seven years undercover as an extension of the disguise? Or had Mark Kennedy, straight-arrow son of a traffic policeman, always hankered after a bit of ink? And if the latter was the case, what might that tell us about his psychology?

It wasn't the only question that remained unasked in Brian Hill's film about the case. And while it would have been naive to expect answers to everything (there's still no agreement about how much Kennedy's seniors knew about what he was up to), the word "confession" in the title did seem to hint that we might penetrate a little deeper into the motives of the man himself. What about Kennedy/Stone's beliefs for example? Presumably when he started his operation, he bought the official line that intelligence was needed to plan a proportional response to demonstrations. He may even have believed that the groups he infiltrated represented a real threat to democracy. But what happened after years of living with activists, and falling in love with one of them? Did he begin to think that their arguments made sense? Was he ever tempted to turn double agent? He wasn't asked.

"I liked the life that Mark Stone had but I enjoyed the job Mark Kennedy did," he said at one point, a remark that suggested he was getting thrills at both ends, licensed to walk on the wild side, but still getting approval from authority. So, what kind of relationship had he had with his father, I wondered, and how might that have fed into the dangerously doubled life he found himself living. Again the question wasn't put. Instead, we got a narrative that concentrated on betrayal and stress and contradiction, but didn't burrow deep into the sources of a betrayal that has pretty much ruined his life. It certainly wasn't dull – the story is like a crusty's retelling of Conrad's Under Western Eyes, with its tragic collision of power politics and private passions. And there was a pathos about where Kennedy has been left – rejected by all sides, and hopelessly nostalgic about the comradeship of the people he lied to. But I think it would take a dramatist to get to the real heart of the tale. I'd suggest the first scene is set in a tattoo parlour.

I wish the BBC would stop making its presenters open up their new series with bombastic hype for what's to follow. At the beginning of Art of America, for example, Andrew Graham-Dixon said this: "The story of American art is as epic as the story of America itself." Really? American art found itself intervening in two world wars did it? American art suffered through a bloody four-year civil war in which brother found himself killing brother over the importance of impasto? It was one of those sentences that seemed designed to goad you into grumpy contradiction. And the really irritating thing is that as soon as the presenter is allowed to start saying what he really thinks the script becomes far more alluring. Tellingly, Graham-Dixon's best lines attested to the less-than-epic quality of early American art. He summarised early portraiture as "the not-quite Van Dyck, the nearly Gainsborough" and described the grand historical paintings in the Capitol as being "depicted with all the panache and excitement of a school photograph". It's full of good things, but I suggest you turn up two minutes late.