“Nothing is predictable about the British weather; that’s why we love to talk about it.” Well, yes, but you still wouldn’t expect it to be the subject of a West End thriller. Pressure is a play about trying to second-guess the English weather, with tens of thousands of lives at risk. If you’re thinking of something like The Day After Tomorrow, think more about the day before yesterday. About 1944, in fact, when the Allies needed to know if conditions would be suitable for the D-Day landings.

Matters hinged on a dour, edgy Scotsman, Group Captain James Stagg. Stagg was one of the few meteorologists at the time who paid attention to high-level air movements, and he realised that a storm was on the way to the English Channel on the designated day of 5 June; his American opposite number maintained that all would be fine, but Stagg eventually won over General Eisenhower and the other Allied commanders to postpone the invasion. Then the same attentiveness led Stagg to believe that the weather would shortly clear, and Operation Neptune could probably go ahead the following day. Amazingly, John Dove’s unfussy production manages to elicit real and increasing suspense from people poring over wall-sized weather charts, occasionally drawing on a new isobar.

Stagg is played by David Haig. The character’s irascibility... and, indeed, his Scottish accent... are some way away from Haig’s usual, warmer territory, but he knows how to get under the character’s skin. He ought to, after all, having written the play as well. The thing is that Haig never writes plays simply as vehicles for himself. His first, My Boy Jack, was about Rudyard Kipling’s grief for his son who died in WW1; The Good Samaritan drew on his own sometimes harrowing experiences as a Samaritans phone counsellor. Pressure is about not just an unsung hero but an aspect of World War Two that’s almost entirely overlooked. In the end, this man who spent his time alternately grumbling at colleagues and fretting about his wife going through a difficult labour miles away saved untold lives.

Nor does Haig the writer make it a one-man show for Haig the actor. Philip Cairns gets a rather raw deal as American forecaster Krick, but the character of Eisenhower is a fine creation, particularly in the second half as the invasion draws near and takes place; Malcolm Sinclair runs pretty much the full gamut of emotions with skill and sensitivity. Laura Rogers provides some sorely needed female focus as Eisenhower’s factotum and, implicitly, lover. You end up thinking twice instead of automatically chuckling when Stagg asks, “How could the weather ever be boring?”

Written for The Lady.