The Law of Instant Contradiction is one of the more reliable principles of comedy - the law holding that laughter will be directly proportionate to the rapidity and vigour with which a statement is shown to be wrong. There was a fine example in last week's episode of Operation Good Guys, BBC 2's enjoyable spoof of a fly-on-the-wall documentary about a squad of police officers. DI Beach, stung by criticism of his team from a visiting NYPD detective, is angrily reminding his guest that they are a hand-picked elite: "What you see out there is the top three per cent," he says forcefully. This claim is interrupted by the boom of a money-dying device going off in the next room, one of his younger officers having been unable to resist the temptation to take a peek at half a million dollars intended for a sting operation. For the rest of the episode the elite wander around covered in indelible silvery paint, including one officer who covered his face at the critical moment and thus sports a perfect outline of his hands. And given that such documentaries depend on intercutting live footage with arranged interviews it's understandable that Operation Good Guys makes fairly heavy use of this device - the victim usually being DI Beach, the senior officer, who has to spend much of his camera-time putting positive spin on the unfailing incompetence of his team (Beach is wonderfully played by David Gillespie, incidentally, in an understated performance that exactly catches the paste-on confidence of the middle-manager under pressure).

One of the more reliable laws of television reviewing is that when you finally get round to reviewing a series you like a lot the episode will be slightly below par. This week the squad had been given a day off and the writers succumbed to the temptation to relax their own discipline a little, too. In previous episodes the relationship between Beach and his next-in-command DS Ash had been very delicately sketched, the mutual need of a natural disciple and a deference junkie; but this week the two men went on a shopping spree in the West End which was presented as a gay falling-in-love sequence, the kind of pop-song montage that is popular in Hollywood movies. Not only was the idiom awry but the sequence felt untrue to the characters. But there was still evidence of the writers' ability to build surreal absurdity out of entirely credible components - most notably the moment when one of the team had to read a man his rights in a voice made squeaky by helium inhalation (it would take too long to explain, but the sequence of events leading up to this was perfectly plausible). On form, it's fresh and funny - more evidence (along with the recent Alan Partridge series) that BBC Comedy is increasingly capable of real invention.

Scrutiny: the Class of 97 offered a genuine observational documentary, one which followed five new MPs through their first months in Parliament. Even with real material, a canny director will be on the look out for opportunities for a mocking cut from wishful theory to grubby reality, and there was no shortage here of the first half of the combination. You imagined it would be relatively easy to find a vivid contradiction of Nicholas Soames' grandiose assurance that ministers like nothing better than to have their ear bent late at night by unknown backbenchers. Similarly when Julie Kirkbride insisted "I don't feel a burning desire to move up the greasy pole, I really don't", it was hard to prevent the imagination supplying a rebutting image. You didn't see such a thing on screen, naturally, but that wasn't the fault of the producer Anna Lloyd. All five of the people here are ambitious young politicians and so the amount of unguarded candour was bound to be vanishingly small. What exactly do you expect a Labour new bug to say when he is asked by a school child whether Tony Blair is a "nice person"? As Clive Efford pointed out, shortly after a tantalising hint that he had delivered opposition members to compromising destinations during his time as a cabbie, the truth will have to wait until they all retire and write their memoirs.