“We shall fight them on the beaches, in the streets and in the hills”. Or maybe we won’t fight them at all. That knife-edge moment, when Britain chose whether to fight or fall, is the focus of Darkest Hour. Churchill is the new Prime Minister. But his biggest battle is not with Herr Hitler – it’s with his own cabinet. The nation’s fate rests on Churchill’s personality. And it’s a tense, funny and surprisingly cinematic encounter.

A film smothered in cigar smoke and talky tension, this could’ve been a stifling experience. That it’s not is down to director Joe Wright (Atonement) and to a mesmerising central performance from Gary Oldman (Tinker Tailor).

The West Wing with waistcoats this isn’t. Darkest Hour gives double value. A well-woven script, roots us in the reality of the moment; no revisionism here (as with last year’s misfire Churchill). Wright imbues it with a visual truth that makes the film well worth seeing on the big screen.

In a signature tracking shot, Churchill’s journey to the Palace takes in a slo-mo bustle of humanity. At times, the camera sweeps up from a grounded viewpoint - a doomed soldier, a child – to reveal the wider war, flashes of fire carpeting across the screen. All the while, Wright’s five-time muse, Dario Marianelli, scores the film with thrumming rhythms and musical jokes, capturing Churchill’s character and crisis.

Oldman gives an Oscar-worthy, multi-layered performance – literally so, underneath Kazuhiro’s Tsuji’s flawless latex. He’s funny, vulnerable, and pugnacious. “Will you please stop interrupting me while I’m interrupting you” he shouts, capturing the self-aware anger and humour of the man. With his long-suffering wife, Clementine (Kristin Scott-Thomas), you believe the tender strength of their history together.

Bawling out his new PA (Lily James, Cinderella), then bonding with her, you see in Oldman the cost of what’s at stake. With Chamberlain (Ronald Pickup, excellent) and the Foreign Secretary (Stephen Dillane, equally so) plotting his downfall, and a peace deal with Mussolini, Churchill’s isolation is vividly rendered, framed in doorways and lifts. A brilliant, long-held shot sees Churchill bathed in angry, portentous red light, delivering his first radio address to the nation. It’s a searing, heart-catching moment.

Lighter moments still pack a punch. Kissing the monarch’s hand, Churchill doesn’t see that he wipes it afterwards. Aussie actor Ben Mendelsohn (Animal Kingdom) conveys the King’s conflicted dignity in every intonation and movement. David Strathairn (Good Night and Good Luck), gives a pitch-perfect comedy cameo as President Roosevelt, a laugh-out loud scene that also underscores Churchill’s friendlessness – a V-sign to the ‘special relationship’.

Not everything works. Wright’s attempt to externalise Churchill as in-tune with the public, sees the fish out of water PM on a tube train asking plucky Londoners if he should give in. Done with humour it still sticks out in an otherwise subtle film.

When many associate Churchill with a nodding dog on a dashboard, this is a vivid, timely and gripping depiction of a man, and a moment, that changed our history.

Darkest Hour is a reference not so much to the nation’s fear - since as the film points out, most people in Britain were kept largely innocent of the real state of the war - but to the political crisis of confidence in the early summer of 1940 that could have seen the subjugation of Britain and its empire.

This is a strong and mostly accurate depiction of the events of a few weeks in 1940: Churchill was trying to achieve and retain power, not just for his own sake, but because of the real possibility that if he and his fragile cabinet fragmented or failed, Britain could end up with a government that would sue for peace with Hitler.

Churchill is played here by Gary Oldman (and what an interesting choice of lead actor!), with the sort of spark that makes it possible to believe that this man had been involved in a cavalry charge at Omdurman, had tried to transform the Great War with an invasion of the Dardanelles, had tried to turn back the tide of the Russian Revolution, and had already spent a long career making headstrong and controversial decisions in war and politics.

There are many great performances here. Kristen Scott-Thomas is a sympathetic and realistic Clementine Churchill, trying to support an eccentric and aggravating husband at a time of crisis. Ben Mendelson is superb in a (necessarily and appropriately) undemonstrative and quiet performance as King George: in face, voice and character, he fits the bill beautifully. Veteran of stage and screen Ronald Pickup is an utterly convincing Chamberlain, tired and ill, but no less patriotic and concerned about his nation than his rival.

Much has been made of the ‘ahistorical’ scene where Churchill escapes his official car to travel by tube to Westminster, and like Henry V doing the rounds on the night before Agincourt, he gets to encounter ordinary Londoners to gauge their morale. This, and the subsequent scene in the Commons, turn into a strongly jingoistic episode which perhaps doesn’t sit entirely well with the more thoughtful and subtle film that goes before.

Maybe the tube event didn’t happen in quite this way and at this time, but it is well documented that during the 1941 blitz, Churchill used to madden his minders by heading off on unauthorised walks around London’s streets – he really did try, sometimes clumsily, to connect with the people he was trying to lead.

So, there is nothing inherently improbable about his actions here, and the same is true of other points where the film departs from history: the film sometimes embellishes and embroiders truth to get to the nub of its story, just as Churchill did to hold his government together in 1940. Very appropriate.

World War II is a great source of lionisation for the Western hemisphere. Where the Americans have the D-Day landings, the British have Dunkirk. Dunkirk represents a Great British myth; the victory snatched from the jaws of defeat. Already explored last year in both Christopher Nolan's visceral, devastating epic and Lone Sherfig's Their Finest, there is now Darkest Hour, taken from the perspective of events in Westminster, as well as doubling as a biopic for Winston Churchill.

The film focuses on May 1940, and the extraordinary events that took place. We start with the resignation of Neville Chamberlain, take in the creation of Churchill's war cabinet and the turmoil this caused, before climaxing with (spoiler alert) the successful evacuation of Dunkirk as Western Europe falls. All of this is seen from the perspective of Churchill and those closest to him.

After the presence of Churchill in several high-profile costume dramas in recent years (most notably The King's Speech and The Crown) you would imagine there is not a great deal left to be explored. Darkest Hour doesn't ever really sell itself as a new look at Churchill. But what it does gives us is a simply sensational performance from Gary Oldman. Behind layers of make-up and latex (credit to the team behind this as it is very effective) the actor turns Churchill into a charming outsider, conveying the inner dilemmas of the wartime leader as well as bringing a surprising amount of charisma to the part. Oldman has rarely been better than is he is here (I hold a special place for his volcanic performance in Leon and he is quietly brilliant in Tinker Taylor Soldier Spy) and the actor is rightly the frontrunner to be crowned Best Actor at next month's Oscars. Oldman is not quite the Churchill we are familiar with but successfully crafts a three dimensional, living interpretation.

The actor is ably supported by a great cast. Lily James is an effective conduit for the audience, with Winston first introduced through her arrival at his estate as his new secretary. Kristen Scott Thomas doesn't have a great deal to do in the supportive wife role but has a fabulous chemistry with Oldman. Ben Mendelsohn makes a fascinatingly repressed George VI, the actor doing a great deal with slim material. You could easily reuse this cast and create a series of films on Churchill's life from the end of the film.

Joe Wright directs with aplomb (bouncing back from the regrettable Pan) turning the film into a claustrophobic wartime thriller, as well as a powerful biopic. Darkest Hour is certainly heavily biased to the idea that Churchill was a brilliant man, and is mostly a slice of propaganda. But it is so very well made, from a snappy screenplay by Anthony McCarten to an impactful soundtrack from Dario Marianelli. There is a risk that the film is too stylised, but it makes the film particularly engaging, preventing it from being too dry a viewing experience.

I had a surprising amount of fun with Darkest Hour. The film has a great humour that offsets the fact it is mostly a series of scenes showing men in dank rooms arguing and staring at maps. The film even works as a fascinating companion piece to Dunkirk, adding colour to Nolan's ferocious work. With an exceptionally good lead performance and a director confidentially back on form, Darkest Hour is exceedingly good propaganda.