The new Lily Allen vehicle opens in a spruced-up terrace in the East End. Allen plays a self-satisfied yuppie, Jenny, whose cynical husband has invited two ghastly friends over for a bitchy booze-up. At first sight this looks like a Hampstead comedy from the 1970s but it’s a horror story, and it has a huge black hole at its core. A classic horror yarn should be driven by a single, powerful premise. In Ira Levin’s Deathtrap, a failing playwright has to bump off a talented rival to restore his fortunes. In Psycho, a bland motel is terrorised by a deranged and violent loner. Even Shakespeare dipped into the horror genre.