In an early scene in Darkest Hour, Clementine Churchill tells another character that her husband is “just a man, like any other”. This is a knowing opening joke in Joe Wright’s new film about May 1940 and the first three weeks of Winston Churchill’s premiership. It is a joke that just about everyone is guaranteed to get. Even those of its citizens with the slenderest grasp of this country’s past will know that Churchill was not a man like any other. During its long and rich history, Britain has had good, bad and mediocre leaders. Churchill occupies an elevated plinth all to himself as the prime minister who led his country through a struggle for national survival, the like of which it had never before endured and has never since experienced. The stakes were vertiginous when he replaced the discredited Neville Chamberlain at Number 10. The choices made in the early weeks of Churchill’s premiership were a hinge point in history. In play was not just the freedom of Britain but the future of an entire continent.

This makes the Churchill legend one deserving of his country’s pride and at the same time it presents us with several linked problems. He is a challenge for actors who try to embody him and for the politicians who have followed him. There is also a Churchill conundrum for the country that remembers – and misremembers – his role in its history.

Let’s start with the actors. Their portrayals of Churchill matter. As the wartime generation fades away, more and more of us will only know him – or think we do – from the versions we see on screen. Some of our finest actors have given it a go in recent years. There was a cameo Churchill from Timothy Spall in The King’s Speech, which was rightly chastised for taking some liberties with the history of his relationship with the monarchy. John Lithgow offered an empathetic Churchill in his second, peacetime, period as prime minister for the Netflix series The Crown. Michael Gambon gave us an affecting portrayal of the great man in decline in ITV’s Churchill’s Secret. He was never seen on screen during Christopher Nolan’s Dunkirk, but a Churchillian spirit infused that immersive account of the British army’s narrow escape from France in 1940. Brian Cox was a jowl-quivering Churchill in last year’s film of the same name, which presented him not as the imperturbable war leader but as a man tortured with agonies about the risks of attempting the 1944 Normandy landings.

Darkest Hour also has an ambition to peel back myth and find the complex character within. Wearing a fat suit and a lot of prosthetics, Gary Oldman’s impersonation is sufficiently spirited to shine even through layers of latex. This film doesn’t avoid all the Churchill cliches. There is a lot of cigar-chomping and whisky-swilling. Despite that, Oldman succeeds in creating a Churchill who is more interesting than the “bulldog” of simple legend. We see him courageous, martial and inspirational, but also beleaguered and uncertain, playful and earthy, fearsome and maudlin, cunning and loving, bad-tempered, sentimental and tearful. We are reminded that the superman was, just as his wife said, a man. He was a genius not because he was without faults but because he transcended his flaws. This is what makes him such a remarkable example of the human species.

And such an intimidating challenge to each politician who has followed him in Number 10. At some level, every prime minister since has known that they will never match his place in history. In today’s rather baleful political scene, he is more than a challenge –he is a rebuke.

We pine for politicians who aspire to do more with language than marshal banalities, incite division and rouse nastiness

The recent burst of film-making about the 1940s may be mainly because the period provides such strong material. I suspect something else is going on: a feeling that there is no one like Churchill – or anywhere close to being like him – among contemporary political leaders on either side of the Atlantic. It is our misfortune to be passing through a period when the worst sort of leader uses passion in the service of malevolence while the better types struggle to articulate much by way of uplifting conviction. Do we have a yearning for leadership that combines principle, vision and humanity with the capacity to mobilise and unify people behind a collective and heroic endeavour? I rather suspect we do.

We surely also pine for politicians who aspire to do more with language than marshal banalities, incite division and rouse nastiness. Darkest Hour pivots around three of Churchill’s finest speeches: his debut to parliament as prime minister, his first radio address to a frightened nation and another speech to MPs following the Dunkirk evacuation. In that short span of just three weeks, Churchill produced a triptych of some of the most influential feats of 20th-century oratory when, in the words of Edward R Murrow, “he mobilised the English language and sent it into battle”.

It would be unreasonable to expect today’s politicians to match the Churchillian style. His lavish orotundities and bombastic circumlocutions are stirring in a historical drama but they wouldn’t suit our period when television and social media are the principal environments in which contemporary politicians must operate. That said, his most memorable phrases resonate down the decades because they are timeless in their potency and so much better than anything to be heard from politicians of this age.

“I would say to the House, as I said to those who have joined the government: I have nothing to offer but blood, toil, tears and sweat.”

“You ask, what is our aim? I can answer in one word. Victory. Victory at all costs. Victory in spite of all terror. Victory, however long and hard the road may be, for without victory there is no survival.”

Kristin Scott Thomas and Gary Oldman as the Churchills in Darkest Hour. Photograph: Allstar/Working Title Films

“We shall fight on the seas and oceans. We shall fight with growing confidence and growing strength in the air. We shall defend our island, whatever the cost may be. We shall fight on the beaches, we shall fight on the landing grounds, we shall fight in the fields and in the streets, we shall fight in the hills; we shall never surrender…”

Never in the field of human conflict was so much owed by so many to one man’s brilliance with words.

Compare and mournfully contrast the power of his oratorical poetry with a Donald Trump tweet or Theresa May coughing her way through a conference speech or Jeremy Corbyn having a bit of a rant or Jean-Claude Juncker on a verbal ramble at a Brussels news conference. Inasmuch as contemporary political players pay homage to Churchill, it is the dismal tribute of offering bastardised versions of his wartime rhetoric in self-serving support of their own causes. Mrs May does this with her awful “red, white and blue Brexit”.Boris Johnson does this when he claims that Britain will become “a vassal state” if it doesn’t have a relationship with the European Union that he approves of.

How painful it is to contrast what was at stake in 1940, when there was a genuine danger of Britain becoming “a vassal state” of Nazism, with the phoney and petty furies that foam around many of the arguments related to Brexit. The current cabinet bickers about whether Britain should aspire to be Canada plus or Norway minus. What wretchedly pathetic wrangling compared with the awesome choice facing Britain when Churchill became prime minister.

Hitler had swallowed Austria and consumed Czechoslovakia. Poland had been devoured by Nazism in diabolical compact with Stalin’s Soviet Union. Denmark and Norway had been gobbled up too. Belgium, Holland and France were overrun within a month of Churchill’s arrival at Number 10. The military situation facing Britain looked catastrophic. Consideration was given to evacuating George VI and the royal family to Canada. The Americans were sitting on their hands. In an excellent scene in Darkest Hour, Churchill is on a bad transatlantic phone line to Washington to beg help from Franklin Roosevelt. The American president is all sympathy and no assistance. He can give only excuses for inaction. The Americans are even reluctant to release planes that Britain has already paid for.

To fight on – or to take up an offer from Mussolini to mediate a peace with Hitler? That is the grave question around which revolves the political drama of Darkest Hour. The film reminds us that the choice made by Churchill was not at all obviously the correct one to many of his colleagues. He began his wartime premiership as a much distrusted figure within the Tory party. Though it later suited everyone to pretend that he was the inevitable choice as prime minister, a significant number of his colleagues thought it should be anyone but him. George VI, who has been treated kindly by recent film and television productions, was among the Churchill sceptics.

Chamberlain (Ronald Pickup) and Viscount Halifax (Stephen Dillane) are accurately portrayed agitating for Britain to take up Mussolini’s offer. One of the things to like about Darkest Hour is that it does not depict them as cartoon appeasers of fascism, but as men sincerely convinced that fighting on will be national suicide. To them, Churchill’s fine rhetoric is beside the point compared with the power of Hitler’s weapons of destruction. “Words and words and only more words,” sneers Halifax. He was wrong, but he was wrong for reasons that seemed compelling to many people in May 1940. Much of the British military thought invasion highly likely and defeat unavoidable. This context makes Churchill’s determination to fight on all the braver.

Here the story of his leadership folds into our national legend to create a collective memory that has always set apart Britain from its neighbours. For most Europeans, 1940 will always be a darkest hour. The majority of the continent was either celebrating Hitler or allied to Germany or conquered by the Third Reich or would be soon occupied. For Britons, 1940 became a finest hour. It was retrospectively bathed with a fierce patriotic glow as the year when this country stood splendidly defiant – “very well, alone”, as the great man put it. This has made a major contribution over the decades since to a strong strand of British exceptionalism that has inevitably infected the argument whenever we have debated our relationship with the rest of Europe.

Crowds follow Winston Churchill as he inspects bomb damage in London in September 1940. Photograph: Fox Photos/Getty Images

Yet 1940 has never represented a case for Britain to be detached from its continent. Churchill understood that. It is central to his historical importance that he saw this much more clearly than Chamberlain and Halifax. He argued for fighting on because he grasped that Britain’s fate was entwined with that of its continent. Making peace with Hitler would mean surrendering Europe to the barbarity of Nazism. On 18 June 1940, in the wake of the capitulation of France, he told the Commons: “Hitler knows that he will have to break us in this island or lose the war. If we can stand up to him, all Europe may be free and the life of the world may move forward into broad, sunlit uplands. But if we fail, then the whole world, including the United States, including all that we have known and cared for, will sink into the abyss of a new Dark Age made more sinister, and perhaps more protracted, by the lights of perverted science.”

He took this stance in the face of considerable public terror about the consequences of fighting on. The most irritating scene in Darkest Hour is one that is entirely made up. At the height of the war cabinet’s debate about whether to sue for peace, the film-makers put Churchill in a London underground carriage where he asks a selection of salt-of-the-earth Brits whether he should open negotiations with Hitler. To a man and woman, adult and child, they all respond “never”. This invented scene is seriously misrepresentative of public opinion in May 1940. Many Britons were very fearful, and understandably so, of carrying on the war. It had not been that long ago that crowds thronged to cheer Chamberlain when he returned from Munich with his bogus “peace for our time”.

Britons were still scarred by the meat-grinder carnage of the trenches of the first world war. The advent of airpower – “the bomber will always get through” – added to the horror of a conflict of indefinite duration that the country could not be at all confident of surviving. It was really only after the unexpected deliverance at Dunkirk and during the Battle of Britain that followed that the nation solidified behind Churchill’s view that there could be no compromising with the menace of Nazism.

This is one of the many aspects of Churchill to admire. When he started to deliver his fighting speeches, he couldn’t be sure that he would carry Britain with him. He did not tell the public what they all wanted to hear; he used his powers of advocacy and inspiration to rally parliament and the people behind him. He did not follow public opinion. He led it. That is at the heart of his magnificence. It is also another reason to mourn the lack of contemporary politicians who aspire to emulate his example.

Darkest Hour opens on Friday