It’s not much of an exaggeration to suggest that new plays by up-and-coming talents are something of an Achilles heel at the National Theatre. Even Mike Bartlett’s much lauded Earthquakes in London was a far more exciting production than it was a play, while Greenland proved so devoid of audience that it was pulled early from the schedule. The latter did no favours to anyone by yoking together four dramatists including the impressive Penelope Skinner. Now four more emerging playwrights have been given their head but this time their voices remain distinct in the two double bills that comprise Double Feature.