Earlier this decade we all watched as France entered one of its terminal historical crises. Now it is Britain that has lost definition – or should that be England, or the United Kingdom? No longer can a national intellectual such as George Orwell set down a few thoughts about our aversion to conscription and fascism and our liking for a drink, as he did in 1941 in The Lion and the Unicorn, and we will all nod because we recognise ourselves. What united the inhabitants of Grenfell Tower with the billionaires of Kensington Palace Gardens and the parishioners shuffling into the church of St Mary Abbots every Sunday, other than their residency of the same London borough?

John Major’s “long shadows on county grounds, warm beer, invincible green suburbs” were greeted with sniggers when the Tory prime minister brought them up in a speech in 1993 (he also mentioned Orwell). Nowadays we measure ourselves against flattering abstractions – liberty, enterprise, tolerance – but these are universal values and may be found more abundantly elsewhere. Only as individuals, or as groups holding little flags of race, gender or sexuality, can we put who we are into words.

Now we have Brexit to contend with and the pessimists think it will break us. Break what, exactly? Ask the historians, for the job of history is to explain our kinship with others and the structures that keep us civil. Here are two very different books to help us through our predicament of botched renewal and recrimination.

David Edgerton’s The Rise and Fall of the British Nation is for the most part a fierce and dazzling account of 20th-century Britain from the perspective of a historian of science and industry. As befits an opponent of “declinism”, a syndrome that exaggerates Britain’s fall from grace before proposing implausible “solutions”, Egerton spends the best part of 500 pages arguing that things haven’t been all that bad. Then suddenly, like a cyclist defeated by the final, brutal ascent, he collapses in a heap of cynicism and despair.

Edgerton’s modern Britain didn’t emerge from the empire (itself a pretext for protectionism through imperial preference) but from free trade. In the Edwardian era almost anything could be imported into Britain duty free. The “full English” was made up of Danish bacon, Dutch eggs and bread from Argentinian wheat. Cotton came from the US, iron ore and timber from the continent. “Buy British”, the mantra of more recent years, when domestic agriculture and manufacturing huddled behind tariffs, would have been meaningless.

Beginning in the 1930s, accelerating after the second world war, this changed. From the introduction of national service to protection for car-makers and the rhetoric of nationalism employed by the Attlee government, Britain became more like the nation states of continental Europe. Here, then, is the “rise” of the “nation” – set to a jingoistic score. “We now have the moral leadership of the world … and we shall have people coming here as to a modern Mecca, learning from us in the 20th century as they learned from us in the 17th.” The patriot who uttered these words was Nye Bevan, who was well to the left of Attlee and set up the National Health Service.

Causing more national angst than any other institution, the NHS is the undisputed symbol of postwar Britain. Edgerton is disrespectful of the myths. Both major parties exaggerated the resources that went into its establishment in 1948, he finds – the Conservatives alleging waste, Labour boasting of social justice. In fact the cold war and Britain’s obsession with punching “above its weight” meant that it was defence spending, not welfare, that consumed 10% of GDP in the early 1950s – including Attlee’s short second ministry, when Bevan resigned as minister of labour in disgust at the introduction of charges for false teeth and spectacles to pay for arms. In the 1970s Britain’s “warfare state” was better financed than either education or health.

The reader is introduced to declinism as decolonisation proceeds and the nation searches for its USP. Orwell has plausible paternity but Edgerton rounds on CP Snow, who in 1959 famously alleged an elite bias against science and expertise. Nonsense, Edgerton retorts, and he reels off the names of boffins with influence over policy, but the truth is that a lot of costly technical projects failed. Britain’s “independent” nuclear deterrent was abjectly reliant on American technology. Not a single foreign airline bought Concorde. Much postwar mass housing was so shoddy it had to be pulled down.

On the wider question of national failure Edgerton argues that Britain’s pre-eminence in the world was inevitably brief; “the others” were always going to make up the difference. Even then we didn’t just curl up. Our war effort was much more efficient than the prevailing image of Colonel Blimps would have us believe (the subject of Edgerton’s earlier book, Britain’s War Machine). As late as 1950, Britain retained one quarter of the world market in manufactures; between 1950 and 1984 there were just two years without a British Nobel prize. But through the 70s the achievements get fewer and less substantial.

Edgerton’s penultimate chapter, A Nation Lost, is about Thatcher’s Britain. She inherited, “uniquely in British history”, a nation self-sufficient in food and – thanks to North Sea oil – about to become a net energy exporter. She left behind a net importer of manufactures whose assets had been flogged, a riven people increasingly captive to European federalism – anything but the socially conservative Britain with a strong manufacturing base in private hands that she seems to have wanted. Thatcher planted the “bullshit Britain” that was harvested by Blair, a polity simultaneously capable of and vulnerable to centrifugal separatisms even as it encourages “fantasies of transformative revival and distinctiveness”.

It is a measure of declinism’s grip that, for Brexiters, leaving Europe is the only way to escape it, while for remainers the same course of action will make it worse. Edgerton prides himself on being immune – which makes his final bilious pages all the more disconcerting. “Only satirists, not historians, could do justice to this turn of events” is his last line, referring to the spectacles of Blair working for dictators and a state funeral for Thatcher. Hearken to the sound of an intellectual throwing in the towel.

Fantasy or not, revival and distinctiveness are essential to optimism and they figure prominently in These Islands, Ali Ansari’s pithy and elegant essay in support of Britishness. Orwell’s paw prints are again everywhere (the title is from The Lion and the Unicorn), but Ansari sides with Orwell the sentimentalist, not Orwell the revolutionary. His outlook is cautiously Whiggish and patriotic, defending the empire as not as bad as the others and reminding his fellow Scots – he is a professor of modern history at St Andrews – of their enthusiasm for an enterprise they now disown. (Early Scottish nationalists demanded acknowledgement from the English of the Anglo-Scottish nature of the empire.) His solution is a programme of public education in Enlightenment values, not any old Enlightenment values, but British ones shaped by our experience of parliament, voluntary association through the union of 1707, tolerance and dissent.

As a first generation immigrant to Britain (from Iran, a place that knows a bit about past glories), Ansari once surprised jaded colleagues by describing his British passport as his most treasured possession. Is it declinist of him to want everyone to feel the same? Can an idea help us back into the habit of belonging together, or is it enough to sell more cars than the French?

• The Rise and Fall of the British Nation by David Edgerton (Allen Lane, £30). To order a copy for £25.50, go to guardianbookshop.com or call 0330 333 6846. Free UK p&p over £10, online orders only. Phone orders min. p&p of £1.99.

• These Islands: A Letter To Britain by Ali M Ansari (Haus Publishing Ltd, £7.99). To order a copy for £6.79, go to guardianbookshop.com or call 0330 333 6846. Free UK p&p over £10, online orders only. Phone orders min. p&p of £1.99.