Last Night's Television: The Persuasionists, BBC2<br />Horizon, BBC2

The Persuasionists, a new sitcom set in an advertising agency, had only been running for two minutes before the hoariest of clichés about comedy got an airing. "It's funny... because it's true," said Greg, looking at a witless copy line for a new campaign. And the fact that this line is given to Greg – one of the dimmest characters on screen – and that he utters it as if it is an observation of great sagacity, suggests a certain contempt for this venerable rule. Which makes sense really because The Persuasionists belongs to that school of sitcom in which things are funny because they aren't true. You could easily write a comedy about advertising that took The Office or The Thick of It as a model, given the rich real world absurdities of the profession. But the familial line here runs back to comedies like Father Ted and The IT Crowd, sitcoms in which any reference to plausibility is disqualified from the start. It might briefly occur to you that as an advertising slogan, "Leave it aaatt!!!" has some obvious drawbacks, but then you remember that the product it's attempting to sell is something called cockney cheese and it seems pointless to quibble.

Comedies like this don't require subtle acting skills so much as inspired clowns. What the jokes need to work isn't emotional or psychological nuance (that sense of truth) but exuberant comic salesmanship. And in this regard, The Persuasionists has one big trump card – the actor Simon Farnaby. Adam Buxton, Daisy Haggard and Iain Lee are all fine – zany and pantomime broad in their respective roles. But as Keaton, the East European "Head of Global", Farnaby is something else besides. Keaton believes in the use of props in corporate life and is convinced that his own business charisma is hugely enhanced by the oversized pencil that he carries around with him. He is also convinced (correctly, it seems) that he is irresistible to women. "You can tell a lot about what someone is like in bed by watching the way they walk through a door," he told an adoring crowd of female account executives, and then proceeded to penetrate the nearest exit with loud and orgasmic cries about how narrow the aperture was. When he's on screen, you forget to fret about the taxonomy of gags and just find yourself giggling stupidly.

When he isn't on screen, things are less assured. Some of the dialogue is awkwardly leveraged towards a punchline, and the other characters will need a more time to bed down into the character predictability that is one element of a successful sitcom. But there's enough going on here, I would have thought, to persuade viewers that it might be worth sticking around long enough to allow that bedding down to take place. Speaking for myself, the moment when Cockney Jim, a gleefully excessive East End stereotype, cried "Gertcha" at the moment of orgasm would have been reason enough to defer a final verdict until later, and give Farnaby yet more time to turn our prejudices – vital for any comedy success – in its favour.

Horizon posed an intriguing and timely question in its episode title, "Why Do Viruses Kill?", and never quite answered it. It did hint towards the end that it might just be clumsiness on the viruses part, since they have absolutely no vested interest in a host that isn't up and about, spattering viral offspring onto elevator buttons and bus handrails. And they also offered a rough sketch of How Viruses Kill, which is by changing uniform so rapidly that the bodies can't recognise what counts as an enemy. But after 50 minutes, the enigmas with which the programme began were largely undisturbed.

That isn't necessarily a criticism of a science programme, which can only patrol the fenceline of current human knowledge. Perhaps we're still broadly clueless in this field. What can legitimately be complained about, I think, is a science programme that stands 30 feet back from the fenceline, delivering elementary instruction in what viruses are and how they operate but very little sense of the most recent scientific discoveries in the field. As is common in popular-science programmes, there was a lot of lining up: we were told that if you lined up rhinoviruses end to end, for instance, you could fit 50,000 across the head of a pin and later someone pointed out that all the viruses on the planet, if laid end to end, would form a line 200 million light years long. Last night's Horizon was fine if you wanted that kind of dazzling fact, something much less technically daunting than the Wikipedia entry on viruses. But if you wanted to know what theories are breeding right now, I think you'd have been disappointed. Lay the really fresh facts contained in this film end to end and they would have stretched halfway across one column of the Radio Times.