David Cameron wisely cracked a joke about saving sketchwriters time by googling Battersea Power Station in advance: as he pointed out, it has been in the Beatles’ “Help” film, in a dalek episode of Dr Who and in Hitchcock’s “Sabotage”. It was also recently used in Ashes to Ashes – a topical gag given the useless Labour attack ads based on the programme.

But Dave missed one obvious gag – here it is.

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