The Weekend's Viewing: The Scapegoat, Sun, ITV1 The Thick of It, Sat, BBC2

One secret of a successful con trick is to never give the mark enough time to think things through.

Go in fast, with bags of style, never for a moment acknowledge the unlikeliness of what you're proposing and the odds are that you can be miles away before you're rumbled. The Scapegoat very nearly bought it off. But then, fatally, it stuttered at the last minute. "We swapped places because of the way we looked," explained the central character close to the end, "and I know that sounds absurd." Hang on, you thought. It really does sound absurd. It is absurd. What the hell was I thinking, letting myself get suckered into this thing?

If you did get suckered in, I don't think you should be too hard on yourself. Because Charles Sturridge's adaptation of Daphne du Maurier's novel made its opening pitch with some brio. Killing time while waiting for a train, John Standing, an unemployed classics teacher, is astonished to meet a man who is his exact double. Johnny, his doppelgänger, is both rich and amoral. He's also bored with his responsibilities running a failing family glass firm. So he steals John's identity and leaves his own behind. When John wakes in the morning, badly hungover, he finds a chauffeur at the door who is disinclined to believe his employer's protestations that he isn't really himself.

Matthew Rhys made John's plight borderline believable, which is usually enough in these things. He keeps thinking that he'll get a better opportunity to make his case, but he also keeps being tempted – by the Rolls-Royce, by the huge country house, by compliant women who appear from around every corner. Johnny, it seems, was a very bad boy and John is tantalised by the opportunity to be a better man than his predecessor. After he's cornered into telling a lie about the business, he finds himself greeted as a returning hero by the factory staff and given the chance to heal the dysfunctional family Johnny has abandoned.

At which point, naturally, evil twin returned for the final showdown. Where Du Maurier left her story open-ended, Sturridge opted for a more conclusive tidying-up, using the glassworks furnace to dispose of the superfluous double and ending with a vision of a restored happiness, as everyone settles down to watch the Coronation. Johnny's mother has kicked her morphine habit (with nothing more than a bit of upper-crust get-up-and-go), his previously wretched wife is pregnant with (we assume) the male heir who will unlock the trust fund, and John doesn't need to look for a job anymore. Absurd, as previously mentioned, but built on a fantasy that may have a grain of truth to it – that it's easier to mend the messes other people make of their lives than the mess you make of your own.

The Thick of It is back, with a coalition government to play with. As you might expect, it's scabrously funny, stuffed with great lines and a pleasure to watch. But – and "but" is not a word I like using about this series – it's also possible to wonder whether it might be suffering from the need to live up to its own reputation. The insults are great, but dialogue that consists almost entirely of insults doesn't quite ring true politically... nor the open contempt and hostility with which the two parties to this arranged marriage treat each other.

I found myself wondering whether there wouldn't have been more comedy in a failed attempt to conceal political differences rather than this gleefully violent expression of them. Peter Mannion's meltdown in front of a class of teenagers didn't convince either, not because you can't imagine a politician knowing nothing about the policy he's launching, but because he would be far more skilled at saying absolutely nothing fluently. That said, it still has more laughs in 10 minutes than most comedies manage in 30.

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