Almeida Theatre, London“What if” fiction as a genre generally explores alternative versions of the past – suppose Hitler had died young or won the Second World War, or that President Kennedy had come through the surgery for his bullet-wounds – but the tool can also be used to explore future possibilities: as Mike Bartlett does in his provocative new play King Charles III, which, as the title indicates, imagines what might happen to the British monarchy after the eventual end of the second Elizabethan age.But whereas counter-fictions about long ago are merely a matter of opinion – who knows what a United Kingdom under the Nazis would have been like? – anticipatory stories are always at risk of being contradicted by history. For example, Bartlett (whose e