Seventeen miles south of Big Ben, and 300 yards outside the M25, the fort on Reigate Hill is a good place to go to contemplate the unhappy state of Britain’s relationship with France. The D-shaped earthwork, which crowns the ridge of the North Downs, was hurriedly thrown up in 1898. It was one of thirteen such fortifications, which were to act as muster points for volunteers in the event of an invasion. Just seventeen years before the outbreak of the First World War, the main threat was thought to come from France – a fact that has a certain resonance today.

In the last years of the nineteenth century a certain type of novelist on both sides of the Channel had fantasised about just such a war. In La Guerre Fatale, published in 1890 and set in 1902, the French land at Deal in Kent. In 1894 in The Great War in England in 1897, William Le Queux envisaged a more ambitious French and Russian assault, along a ten-mile stretch of the south coast. ‘It was too late!’ he writes, after the invaders establish their bridgehead. ‘Nothing could now be done to improve the rotten state of our defences.’ The moral of the story was clear.

In 1898 – the year when Reigate Fort was built – life very nearly imitated art. The face-off came not in Kent or Sussex, however, but at Fashoda, a flyblown outpost thousands of miles away on the upper reaches of the Nile. A few years earlier an enterprising French officer had set out from French West Africa, to exploit the vacuum following the murder of the British General George Gordon by the Mahdists. The French aim was to take control of the headwaters of the Nile and thereby lever Britain out of Egypt, which it had ruled since 1882. The hoisting of the Tricolore at Fashoda galvanised Kitchener’s reconquest of the Sudan. After the British government mobilised its fleet, the French rapidly backed down.

Within a few years the idea that Britain and France might have gone to war over Fashoda began to look absurd. The willingness of hundreds of Europeans to go to fight on the Boers’ side when war broke out in South Africa in 1899 reminded Britain how unpopular it was. ‘We have not a friend in Europe,’ wrote one cabinet minister, who said that the chief problem was that his country looked like ‘an octopus with gigantic feelers stretching out over the inhabitable world.’ In Le Queux’s book, Germany rode to Britain’s rescue; in reality, Berlin was building a navy capable of chopping those tentacles off.

The sense of vulnerability and the rise of Germany formed the backdrop to the Entente Cordiale, which was sealed with two state visits in 1904. It was, from the outset, a shared sense of the German threat that glued France and Britain together – that, and the vulnerability of the colonies of both powers. ‘We give you Egypt,’ said one Frenchman, ‘in exchange for Morocco.’ The former prime minister Lord Salisbury discerned only ‘a mutual temper of apathetic tolerance.’

Through France – and not for the last time – Britain found herself in league with an historic enemy. This time it was France’s ally Russia. Uncertainty in London about quite what the Entente entailed was resolved when in 1914 Germany invaded France through Belgium, which Britain was pledged to defend. By the end of 1914 the British Expeditionary Force had lost 90,000 men, many in the defence of Ypres. But to the south the French had lost ten times more. From then on the British fretted about the state of French morale; the French grumbled about the British not pulling their weight. The imaginative British solution – while a new generation of volunteers was drilled to fight the battle of the Somme – made matters worse. A landing at Gallipoli, designed to knock Turkey from the war and divert German resources away from the western front, looked suspiciously like empire-building to Paris. France’s price was British recognition of her own Middle Eastern ambitions. The British soon rued giving in to this. But then, as one general put it, ‘We have got to keep in with our infernal Allies.’

That thought governed British policy for the rest of the war, and beyond the armistice. In Paris in 1919 Anglo-French relations curdled over whether Britain would let France take over two areas: the Rhineland and Syria, which Britain had recklessly promised to the Arabs as well as the French. The British refused the French demand for German territory, but decided that their European ally mattered more than their new Middle Eastern one: they took the view that before long there would be another war with Germany, which (wrongly as it turned out) they thought they could not win without France.

By the end of 1919, British prime minister David Lloyd George and his French counterpart, Georges Clemenceau, were barely on speaking terms, although their falling-out was concealed from public view. When, after Germany defaulted on its reparations payments and France then occupied the Ruhr, British criticism became strident. Lord Curzon, the foreign secretary, accused the French of ‘seeking the domination of the European continent,’ just as, a century earlier, Napoleon had wanted to.

A spy scandal made matters worse. Late in 1925 the French arrested an ‘artists’ model’ who admitted she had been tasked by three British men with collecting details about French military aviation, presumably through pillow-talk. A French author, Robert Boucard, rushed out a book. In Les Dessous de l’Espionnage Anglais, (the cover of which featured a man in a flat cap grasping the globe) he alleged, among other things, that Lawrence of Arabia and the British military attaché in Beirut were supplying gold and propaganda to fuel the Arab uprising against French rule that had recently erupted in Syria. Boucard claimed to have proof of this, which he had been ordered not to publish, for fear of damaging the Entente.

The upshot was that when the German threat re-emerged in the 1930s, Britain and France did not see eye to eye. The British blamed the rise of Nazism on the Versailles Treaty, and thus partly on themselves. It therefore followed that revision of the treaty’s unjust terms would address German discontent. This was the intellectual basis of appeasement. It was self-deluding and yet also the only answer, given that a series of chancellors of the exchequer, including Winston Churchill, had pared back defence spending, while hypocritically decrying French militarism yet hoping Paris would take up the slack. Although the French connived with the British to let Italy have Abyssinia they were clearer-eyed, realising that atonement would only make matters worse. They understood that for Hitler, Versailles was not a reason, but an excuse.

Rearmament, when it belatedly came, produced yet more friction. The French lacked tanks and needed Britain to make up for this weakness. The British however, prioritised the manufacture of hundreds of Hurricanes and Spitfires. A line of airfields joined the chain of forts: forty years on, the fighter plane was now key to resisting a German invasion. When war broke out the British looked surreally unready: one French civil servant noted with alarm that the editor of The Times (who was a strong supporter of appeasement) had averred just ten days earlier that he was more bothered by the shortage of partridge in Scotland than the situation in Europe.

Early in the First World War a bilingual British liaison officer, Edward Spears, had narrowly averted disaster by alerting the British to the fact the French were withdrawing on their flank. Pressed into service once again by Churchill, now British prime minister, after Dunkirk, in June 1940 Spears flew to Bordeaux, where he hauled a barely-known brigadier named Charles de Gaulle aboard his departing aircraft. De Gaulle served as a useful reminder for the following year that Britain was not fighting entirely alone. Fashoda was, however, one of de Gaulle’s formative memories, and the very pugnacity which made the Frenchman so appealing to both Spears and Churchill soon came back to bite them.

The spark, as previously, was the Middle East, where Britain had bullied one of de Gaulle’s lieutenants into promising Lebanon and Syria, then in the hands of Vichy France, their independence. When, after a short war, de Gaulle took charge in Beirut, he naturally enough refused to honour this commitment, which the British were relying on to serve as a lightning conductor to divert anger at their own continued presence in Palestine.

De Gaulle’s Free French made common cause with Jewish terrorists who shared their hatred of the British and went on to murder Britain’s top official in Cairo, Lord Moyne, an old friend of Churchill’s. Days later de Gaulle and Churchill strode down the Champs Elysées side by side. But by  then the rift was common-enough knowledge: a famous photograph captures them looking in opposite directions. In private, Churchill clearly pressed de Gaulle on whether France had played any role in Moyne’s assassination. De Gaulle insisted not, but that was a lie: there is now plenty of evidence that France provided moral and material support for terrorism up to the establishment of Israel.

That episode sets the Suez crisis the following decade in its true context. In Britain the fiasco is seen as a peculiarly British debacle. In reality, it was a plot dreamt up by the Israelis and the French, which the French then convinced the British to come in on. British relations with Israel were still minimal: without French brokerage, Britain might have been spared the embarrassment of Suez.

The crisis simply laid bare what politicians and officials in London had long known. Britain lacked the money and the energy to support its grand designs. For the French the answer lay in Europe, but their insistence the vision should be signed up to first, and details thrashed out later, put off the British. By the time prime minister Harold Macmillan changed tack and decided to apply to join, de Gaulle was back in power after a decade’s absence. ‘He has grown rather fat; his eyes are bad and he wears thick spectacles’, Macmillan wrote rather cheerfully in his diary. ‘But underneath this new exterior,’ he added, percipiently, ‘I should judge that he is just as obstinate as ever.’

As Britain’s man in Algiers during the war, Macmillan had stood up for de Gaulle against pressure from both Churchill and US president Franklin D. Roosevelt, and no doubt hoped his efforts would be repaid. But gratitude has never played much part in foreign policy, and he soon found out that de Gaulle had an old axe to grind. ‘[I]t all stems from the war,’ Macmillan wrote, in 1960, of de Gaulle’s hostility towards the ‘Anglo-Saxons.’ ‘He resented – rather absurdly in the setting of Vichy and all that – the Roosevelt-Churchill hegemony. He goes back too – in his retentive mind – to all the rows about Syria; about D-Day; about the position of the French army in the final stages of the war; about Yalta (and the betrayal of Europe) and all the rest.’ Vetoing Macmillan’s application, which de Gaulle did in early 1963, was consistent with his view of France’s involvement in the European project. Far from being a futuristic endeavour, it was a way to salvage a measure of French sovereignty and pride.

It was only once de Gaulle was dead that Britain was finally able to join the Common Market. Having joined a club where the rules had already been written, Britain’s antagonistic role was set. Ahead of the UK’s presidency in 1987, the then-prime minister Margaret Thatcher’s adviser Charles Powell was disappointed when preliminary thinking failed to identify ‘a higher profile issue which will demonstrably have you battling for Britain.’ Jacques Delors’s pursuit of a single currency would provide that soon enough.

The unnecessary, if logical destination of European integration, the euro, was also the cause of death of the Entente. In the 1980s and 1990s, through Europe, and the single currency, Francois Mitterrand sought to achieve what the Entente had not: security, symbolised powerfully when he and Helmut Kohl held hands at Verdun during a 1984 ceremony to mark the seventieth anniversary of the First World War. This was a security that Britain, having not recently been invaded, did not feel it needed, but the ‘vision first, details later’ approach to the euro created tensions that ultimately led to Brexit.

Supporters say the European Union has kept the peace since 1957. The reality, however, is that it has not yet been tested. While this remains the case, France has no great need for an alliance with Britain, beyond the day-to-day cooperation that goes on underneath the fractious political relationship. That helps explain the shrillness of French ministers’ recent rhetoric on, of all things, the rights of their fishermen. Fishing rights, it might be reassuring to hear, were also a bone of contention when the Entente came into being. When France feels the urge to renew its always-testy security pact with Britain – that will be the time to worry.