ACROSS the world the British are famed for their obsession with the weather.

David Haig’s new play depicts a day when the atmospheric conditions were vital for the safety of the free world – D-Day.

Pressure covers 72 hours in the nerve centre of the Normandy beach landings – as future president General Eisenhower is presented with two conflicting weather reports.

One, from celebrity US weatherman Colonel Krick, predicts sunshine.

The other, from unassuming Scottish RAF meteorologist James Stagg, suggests a storm is imminent, which could scupper the invasion and kill many soldiers.

Playing Stagg is Haig himself – although he admits he never wrote the part with himself in mind.

“We approached two very famous Scots, both of whom I know quite well,” he says in the week of the play's world premiere at Edinburgh’s Royal Lyceum Theatre.

“They read it and loved it, but were both unavailable. After that everyone turned to me and asked whether I would like to do it.”

Having recently played larger-than-life characters King George III, Prime Minister Jim Hacker, and most recently King Lear, the demure Stagg was a change of pace for Haig.

“I’ve been pushing the boat out with those characters,” he says. “I was looking for a character who was more reserved and reticent.

“I have found the title of the play apt – so the way I have played the part is to imagine the pressure of the event and the decisions he is making and what is happening in his home life at the same time. There's a huge tension and intensity in my version of the character.”

Stagg was facing a difficult position.

Lined up against him was Crick who had made weather predictions for presidents to help organise state visits, and even told David O Selznick which way the wind was going to blow when he filmed the burning of Atlanta in Gone With The Wind. Eisenhower had taken Crick with him through North Africa.

Stagg was basing his predictions on the newly discovered jet stream, a phenomenon only discovered in 1939 through aircraft flight times across the Atlantic, which was ignored by the US meteorologists.

“Ultimately what convinces Eisenhower is the integrity of the man,” says Haig. “He’s taciturn and potentially rude on the surface, but underneath he's quite a hero with this intensity and integrity and a sense of humour which is a relief. It’s an extraordinary thing to tell this story of one of the great heroes.”

The real Stagg is a world away from the pukka Englishman portrayed in Hollywood blockbuster The Longest Day.

“He was the son of a plumber from near Edinburgh,” says Haig adding the Duke Of Buccleuch’s personal plumber had hoped his son would follow him into the trade.

Instead Stagg went to Edinburgh University and joined the Met Office.

It was Haig’s long-time collaborator John Dove who introduced him to the story, having directed the actor’s previous two self-penned plays My Boy Jack and The Good Samaritan.

“John is an unsung hero of British theatre,” says Haig. “We are similar in that we both put our heads down and get on with it, and don't look up until it is finished.”

One aspect of the script Haig was keen to get right was the science.

“I have been in touch with the Met Office from the beginning,” says Haig recalling an extraordinary day when he met their pre-eminent historian.

“When I went up to his room at his club he had all these charts out over his double bed. We drew up two chairs and looked over them for seven hours, going through the script line by line, correcting until hopefully there are no inaccuracies left.

“It’s a headache as I have to churn out numbers and figures which all sound the same to me!”

Alongside Stagg and Eisenhower is a third figure in the story – Eisenhower's driver, secretary and lover Kay Summersby, a figure Haig uncovered during his research.

“I discovered there were two memoirs by Kay about her time with Eisenhower,” says Haig. “One was written while Eisenhower and his wife were still alive, the second was while she was dying of cancer, which was uncensored and she fully admitted to this love.

“She was a great character, but sad, as all the adrenaline and love in her life went into the three years she spent with Eisenhower. When he went into his political career he dropped her and in a sense who can blame him?

“You can see photographs of the two of them together, and there are others from the same places or events where she has been airbrushed out. The three characters of Eisenhower, Stagg and Summersby are the axis of the play. They spend the night of the crossing together trying to kill time like human beings.”

He hopes the intimacy of the Minerva Theatre will add to the play’s intensity.

“It’s the old cliche of the micro and the macro – this small room where the future of the world is played out by these decisions being made,” says Haig.

“Hopefully in the Minerva we can get that feeling across so the audience feels like they are in the room with them.”