In David Haigs magnificent play, Pressure, the Scotsman, Group Captain James Stagg, played by Haig, explains to the American (Colonel Irving P Krick, played adroitly by Philip Cairns) the vicissitudes of the British seaside. It could 80 degrees of blazing sunshine on the beach at 10am. By noon, it would have clouded over. By 2pm, the rain would be rain horizontal but at 4pm, the sun would have come out again as if nothing had happened. Based on actual events, Pressure is the inspired explanation of how crucial the weather was when plans were drawn up to land 350,000 Allied troops on the Normandy beaches. Originally, the date was to have been June 5. Though Krick said that day would be fine, at the eleventh hour, Stagg managed to convince General Eisenhower that two storms in succession would make the landing impossible and the invasion was postponed. But then Stagg realised that the second storm was progressing slowly and there would be an eight-hour gap on June 6 when the operation could, and did, take place. Haigs writing is immaculate. This production whirls along with hurricane force. Haigs performance is a masterclass of precision, subtlety and powerful understatement. Malcolm Sinclair is superb as Eisenhower, never missing a beat and Laura Rogers typifies an era as Kay Summersby, the generals British driver whose world has been subsumed by the war. Plaudits also to Bert Seymour as the fresh faced and ever-optimistic young British officer, Andrew with his wonderful look-on-the-bright-side attitude. Michael Mackenzie for two different roles as the electrician from the Midlands and the upper crust admiral. All the performances (several actors playing dual roles) are strong and create a tightly sealed world. Wherever this HQ was, once there, no one was allowed to leave. Mackenzies telephone engineer says he was chosen for job because he had no family to wonder where he was. If you left without a special pass, you could be shot. Thats how important it was to keep the D Day plans secret. This is edge of the seat stuff. It is also funny. David Haigs televised play My Son Jack in which he also starred (as Rudyard Kipling) was unforgettable for its humanity and pathos. Pressure too is original and inspirational. Haigs finest hour. A great night at the theatre. Pressure is at Cambridge Arts Theatre until Saturday, February 10.