James Graham is a brilliant playwright who has made stage hits out of such unlikely subjects as the football manager Gareth Southgate (Dear England), life in political party whips' offices (This House) and even a 1968 series of obscure American TV debates (Best Of Enemies).

His latest project is a play about the economist John Maynard Keynes, a darling of the Left thanks to his posthumous role in persuading the post-war government of Clement Attlee to borrow big to 'stimulate demand' and 'generate jobs' (never mind that Attlee, like every subsequent Labour government that has followed Keynes's approach, suffered terrible financial crises).

Predictably enough, Graham's play – The Standard Of Living, which will run for 12 weeks from September in the West

End – will concentrate on what has been described as Keynes's 'eye-popping' bisexual love life, rather than his arcane thoughts on macroeconomics and aggregate demand.

'He sh***ed boys all around the world and married a woman. It is really remarkable!' is how Graham chooses to put it.

But is it that remarkable? For me, there is an obvious and clear connection between Keynes's dissolute personal life and his disastrous economic legacy.

I say this for one very simple reason: he spent his life servicing his uncontrolled libido with endless conquests, male and female, pursuing one fling after another and, despite efforts to do so, never having children.

In the same way, his economic thinking urges governments to print money out of thin air in order to achieve immediate political aims.

This stores up all manner of problems – in particular for future generations. Instant gratification is always pursued at the expense of long-term consequences.

'In the long run, we're all dead,' is his most famous and – when you think about it – rather horrifying quote.

And it's only partially true. Yes, in the long run, you will be dead, but your descendants and your society will be left with your unpaid bills – if, as Keynes advocated, a nation's entire political life is built on the principle of borrowing on the never-never.

The director of Graham's play, the august Sir Nicholas Hytner (whose productions include The Madness Of George III and The Lady In The Van) has said: 'What is really touching, really moving, is that he [Keynes] cultivated a healthy shamelessness about sex.' Well, that's one way of putting it. Another is to point out that Keynes was, in fact, a sex-addicted pederast. 

We know this because he openly shared his ghastly preference for under-age sex with the equally libertine members of the so-called Bloomsbury Group, a gang of broad-minded artists, writers and pseudo-intellectuals that included the author Virginia Woolf, the very feeble painter Duncan Grant, who slept with most members of the group, and the historian Lytton Strachey.

They lived lives that were oh-so-daring: conscientious objectors in both wars, deriding Christianity, marriage and all the 'bourgeois' values which Strachey so hilariously lampooned in his elegant writings.

It is in his letters to his sometime-lover Strachey that Keynes was most revealing about his sexual pursuits. In one, he recommended a visit to the fleshpot of Tunis, 'where bed and boy were not expensive'. In another, he declared that Sicily was the place to be 'if you want to go to where the naked boys dance'.

More details of his peccadilloes are contained in his diaries, which contain extraordinary details of dozens of encounters.

There are anonymous encounters with 'Stable boy of Park Lane', 'Sixteen-year-old under Etna' and 'Jew boy' (all the Bloomsburies were shamelessly snobbish and anti-Semitic).

The truth is that Keynes was a lech and hedonist who spent much of his early adult life engaging in sexual relationships with underage partners, many of them conducted – as the economist Saifedean Ammous has pointed out – in children's brothels on the Mediterranean.

His lifestyle underwent a dramatic change in 1921, however, when he fell in love with a Russian ballerina called Lydia Lopokova.

This did not go down well with the other Bloomsburies, especially Woolf, who regarded her as little more than a peasant.

Lopokova was, in fact, highly intelligent and she and Keynes went on to enjoy what was, in many ways, a happy – if childless – marriage that lasted from 1925 until his death in 1946.

It appears that Lydia turned a blind eye to her husband's bisexuality and what it involved. This, presumably, will be addressed in Graham's play, in which Natalia Osipova, herself a Russian ballerina, has been cast in the role of Lydia.

Many might argue that, surely, you cannot link someone's sexual nature with their views on economics. But, of course, you can. Just look at the damage that Keynes wrought.

After the First World War, the Western world was plunged into chaos, revolution and poverty. The condition of the working classes was terrible and in Germany, France, Britain, Italy and the USA, unemployment soared, particularly after the Wall Street crash of 1929.

In this country, thankfully, the Tories, the Liberals and the majority of the Labour Party initially took the view that if you did not pursue 'sound money' – ie money that was not constantly being inflated away – you would suffer super-inflation of the sort that destroyed Weimar Germany in the early 1920s, when people were forced to pay for potatoes and cigarettes with wheelbarrows full of worthless 'Papiermarks'.

Along came the flamboyant Keynes, who had made a huge personal fortune gambling on the international currency markets.

There is a simple solution, he said: let governments print their way out of any difficulties. Only one significant British politician in the 1920s and 1930s supported this bizarre idea: Sir Oswald Mosley, a Labour MP who went on to found the 'Blackshirt' British Union of Fascists.

Mosley's idols Hitler and Mussolini followed Keynes's economic prescriptions to the letter. They thereby destroyed their economies 'in the long run' – and, making good on Keynes's axiom, ended up dead.

Come the straitened post-war years, however, both Labour and the Tories were converted to Keynesianism.

'What's wrong with inflation?' said Harold Macmillan, the so-called Conservative prime minister of the early 1960s, whose brother had an affair with Keynes at Eton.

He was followed by Harold Wilson's two governments, which again produced ruinous inflation, borrowing money as if there were no tomorrow.

But there always is a tomorrow. Finally the men from the International Monetary Fund (IMF) arrived at Heathrow airport in the 1970s and declared Britain effectively bankrupt.

Margaret Thatcher did her best to reverse the trend and establish the principle that governments, like households, should never live beyond their means. But her successors have reverted to type.

I would argue that John Maynard Keynes's central economic idea – that governments should print their way out of national difficulties, rather than balancing the books – was the greatest single cause of Britain's catastrophic decline in the world.

He thought short-term, both in his sexual encounters and in his economics. His teachings should be held up for ridicule in every school and college, just as his proclivities towards adolescents should provoke horror.

The ignorant – and dwindling – band of politicians and economists who still hold his name in awe would do well to reflect on the fact that their prophet was a man whose idea of a personal relationship was half an hour spent fumbling with a 'lift boy of Vauxhall, 16'.