Collaborators, Cottesloe, London Three Days in May, Trafalgar Studios, London Britannicus, Wilton's, London

The playwright can't get started.

The paper is in the typewriter, the story is already mapped out, but the words won't come. This is the dilemma for the dramatist Mikhail Bulgakov in Collaborators at the National Theatre, but not for its author, John Hodge, who gleefully unpicks an alarming footnote in the life of Iosif Dzhugashvili, aka Josef Stalin, and launches it on a flight of fancy.

The Russian dictator's love for the theatre is on record: he saw Bulgakov's White Guard (staged at the National two years ago) 15 times. So too is Bulgakov's commission from Stalin in 1939 to write a play tracing his own heroic youth. From here, Hodge works the dictator's enthusiasm and the playwright's reluctance into a virtuoso fantasy in which Bulgakov's play Moliere spills into real life and Stalin grabs the typewriter for himself, delegating to Bulgakov the day-to-day running of the Soviet Union, with terrible results.

Playing cat and mouse in this gradually darkening burlesque are Simon Russell Beale as Stalin, rugged and coiffured, limping and threatening, playful and steely, and Alex Jennings, airily courageous, bohemian and correct. This star casting coupled with the 24-carat direction of Nicholas Hytner made the show a sell-out before it opened. Crammed into the Cottesloe, Collaborators has no trouble suggesting the literal claustrophobia of the Lubyanka and of the overcrowded Moscow apartment (design by Bob Crowley) that Bulgakov shares with a motley crew, dreaming of coffee, hot water and fruit, and waking in terror from cartoon-like nightmares in which Stalin delivers the fatal blow.

Then there is the other claustrophobia – the feeling that at any moment the men in leather coats will arrive, that blood-test results will be massaged to suit another's purpose, that the freedom given by the allocation of a car and driver is in reality a form of imprisonment. Bulgakov's wife Yelena, played by Jacqueline Defferary, seems to disappear before our eyes, eviscerated by the prospect of grief. There are eyecatching performances too from Mark Addy as the grimly impish secret policeman, and relative newcomers Pierce Reid as an idealistic factory worker and William Postlethwaite as a silenced writer.

The whole Faustian pact hinges on a phone call, many years before, which mysteriously opened doors at the Moscow Art Theatre for Bulgakov. And if the message of Collaborators, that a deal with the devil will bring initial riches and ultimate shame, is not new, this high-voltage knockabout, daring in its comedy, is exhilaratingly fast, original and hugely entertaining.

Meanwhile in Blighty, Neville Chamberlain has sought to end Hitler's advance by peaceful means, which shortlived measure has ended in his humiliation and Churchill's assumption of power. In Three Days in May, the new war cabinet is sitting – Churchill, Chamberlain, foreign secretary Lord Halifax, and Labour men Clement Attlee and Arthur Greenwood – and another dangerous deal is being considered. Mussolini might be brought on side, weakening Hitler enough to negotiate with him, if France and Britain were to dip into their colonies collection and hand the Italian fascist Corsica, Gibraltar, Malta and chunks of Africa.

Ben Brown's dramatisation of the days between the National Day of Prayer, with which the play opens, and the despatching of the little ships to Dunkirk has, of course, a terrific co-writer in Sir Winston Leonard Spencer-Churchill. Warren Clarke puffs and splutters favourite epigrams and calls to arms, a walrus in morning dress, elegantly counterweighted by Jeremy Clyde's refined Halifax. Robert Demeger's Chamberlain is a sympathetic figure: like Halifax, he dreads a repeat of the slaughter of 20 years before. Restocking public morale, it becomes clear, will be as crucial as re-arming.

Our view of the Second World War is so dominated by the big numbers – the long years, the losses, the casualties – that it is striking to discover a turning point, not on the sprawling beaches of Normandy, but in a little room, over a few hours, with only five men deciding the future of the planet. And a sixth listening in ... It is the diaries of Churchill's assistant private secretary, Jock Colville, that give Brown his material, and it is Colville who opens the door of the cabinet to us.

Alan Strachan directs with a steady hand this clash of the big beasts, which will appeal to those who, if they did not serve, at least grew up with war recollections. A new generation will be boggle-eyed that a war was won as much with rhetoric as with rifles.

The struggle for power in Ancient Rome is between matriarch Agrippina and her son Nero in Natural Perspective's fast-paced and unsettling modern-dress production of Britannicus, directed by Irina Brown. Incest, murder, betrayal ... the overbearing mother has stopped at nothing to see her boy proclaimed emperor. And boy is the word. In this new translation by Timberlake Wertenbaker of Racine's account of the feud between Agrippina's favourite and his rival Britannicus, the young emperor Nero is gawky and unformed, swaggering like a schoolboy in his dad's clothes; his enemy chews his fingers. Nor does age alone bring wisdom, as Sian Thomas's furious Agrippina shows. Only Nero's counsellor, Burrhus, is shocked by the emperor's impassivity when confronted with another's pain. He has no empathy because he has been cosseted all his life: poor preparation, Racine and Wertenbaker say loud and clear, for leadership.

With terrific performances all round, especially from Jude Akuwudike as Burrhus and Christopher Colquhoun as duplicitous Narcissus, this gripping and crystal-clear production is at once a thriller, a study of jealousy, and a treatise on power and its responsibilities.

'Collaborators' (020-7452 3000, returns only, until new booking period opens 23 Nov) to 31 Mar, with live relay to cinemas nationwide, 1 Dec; 'Three Days in May' (0844 871 7615), to 3 Mar; 'Britannicus' (020-7702 2789), to 19 Nov

Next Week:

Kate Bassett sees whether Michael Sheen's Hamlet is more matter or art

Theatre Choice

One Man, Two Guvnors – the 1960s seaside update of Goldoni's comedy, with James Corden having a blast – is at the Adelphi Theatre, London (0844 412 4650 to 25 Feb). Meanwhile Kneehigh's The Wild Bride, a folktale of devilish abuse and resilience with wonderful, live blues music is now on tour at the Cheltenham Everyman (Mon to Sat).