I made the mistake of catching up with the darkly sumptuous The Crimson Petal and the White just before knuckling down to review this new two-part drama, and it was like moving from fine vintage wine to warm supermarket-brand lager. To begin with, I couldn’t dissociate Ashley Jensen from her perky but dim character in Extras, so the moment she found herself confronted with a game-show-from-hell scenario of committing a murder in return for five million quid, I expected Ricky Gervais to pop up in the next scene, giving her wisecrack-littered advice on what to do next.