The Weekend's TV: Any Human Heart, Sun, Channel 4<br/>JFK: the Making of Modern Politics, Sun, BBC2

Logan Mountstuart's first childhood memory, fans of William Boyd's novel will know, is the sight of his tutor's circumcised penis.

An extreme close-up of this fascinating object might have been an entertaining jolt for a Sunday night audience, settling down to a big-budget costume drama but in Boyd's own screenplay of Any Human Heart for Channel 4 he'd opted for something more numinous and tasteful – the recurring vision the elderly Mountstuart has of himself as a young boy in Uruguay, sitting in a boat as various versions of his older self stand on the river bank and look on. In Michael Samuels's direction of the scene it had a shimmer of magic to it – Logan's old and young arranged in a symbolist's landscape. "Which life is truly mine?" asked the old Logan musingly on a voiceover. "I'm all these different people...all these different people are me."

His reveries had been prompted by a cardiac spasm and a clear-out, echoey memories of the past rising up around him as he sorts through a heap of old photographs and journals. And, barring the young golden-haired child who pops up whenever an image of unsullied innocence is required, the youngest Logan we get is the student who appears first, in his final year at Oxford and still mightily oppressed by his virginity. Eventually, Logan is relieved of this burden by Tess, a buxom local stable girl who has already bedded Logan's best friend but who has a generously unfussy attitude to sexual exclusivity. And having ticked off his own deflowering, Logan can move on to his next ambition, which is to become a writer.

Logan, a callow boy, thinks that Tess is fine for fun but he'll need something more cerebral for the long term, and he finds a candidate in Land Fothergill, an earnest but pretty young socialist who serves, rather erratically, as Logan's conscience. Land, though, eventually recognises that having a conscience by proxy really isn't good enough and when Logan asks her to marry him she turns him down, rubbing salt in the wound with a scornful summary of his career so far: "All you've written is trash... rubbish... you can't believe how disappointed I am". Logan rebounds into the arms of plump Lottie – who isn't Land but brings a lot of it with her – and the switchback profile of Logan's life is established.

It's very beautifully done, swathed in a haze of period cigarette smoke (it occasionally seems as if nobody was allowed on set without a smouldering fag clutched between their fingers) and played with a glum understatement by a fine cast. There is the odd Downton Abbey moment of absurdity (surely nobody conducts a shoot on the front lawn of the family seat, just a few yards from the parterre?) and moments when the compression of the narrative forces some slightly clumsy timeline signposting and celebrity cameos (Logan finds himself alongside Winston Churchill at a urinal at one moment, and giving way on the golf course to the Prince of Wales at another). But the largest problem may be to do with Logan's character, which never seems quite different enough to justify that opening remark. He starts selfish and appears to remain so, casually unfaithful and distinctly self-pitying. And since you know precisely where you're headed – to Jim Broadbent's remorseful retrospective – there's already a premonitory sense of the switchback's most anti-climactic section, when you coast back to your starting point with all the thrills behind you. Life, as William Boyd once said with reference to Any Human Heart, may only make sense when looking back. But if it's to be truly gripping it may be important not to know where it finally ends up.

In JFK: the Making of Modern Politics, Andrew Marr revisited Kennedy's election and took a hobby horse for a canter. Essentially, his argument was that the rot in modern politics – its substitution of glamour and soap opera for substance and policies – all began with Kennedy's surprise win in 1960. Tony Blair kicking back in his kitchen, Nicolas Sarkozy posing for a celebrity magazine with Carla Bruni.... they were all JFKs fault, since he was the first modern politician to understand that style could win out over substance. Or rather his father was – who promised that he would "sell Jack like soap-flakes" and had the money to make it happen. And even if you weren't prepared to ride pillion behind Marr on this theory all the way, the programme was still fascinating, peeling back the airbrushed Camelot facade to reveal the ruthless electoral machinery that lay behind it.

Kennedy's biggest victim was not Richard Nixon – who learnt the lessons from his bruises and eventually won the presidency – but Hubert Humphrey, a radical and brave Democratic politician who was the favourite to win the nomination as the campaign began. Unfortunately, his moment coincided with JFK's and with the rise of television. Smeared by Kennedy associates, out-spent on airtime and out-bribed behind closed doors, Humphrey lost, though only narrowly. The best bit – apart from Marr's relish for the nitty-gritty of American politics – was the extended play for Kennedy's jingle-led television promo, a maddening ohrwurm in which the chorus assured voters that he was "A man who's old enough to know and young enough to do". I'm still inclined to think that the connection between Kennedy and celebrity politics was an accident of timing rather than cause and effect, but it was good to watch a programme you could have a grown-up argument with, rather than simply heckle.

t.sutcliffe@independent.co.uk