Weeks ago, Scandinavian Airlines pulled a broadcast ad that showed the region’s identity as a magpie mix of cultural influences. Entitled “What is truly Scandinavian?”, the ad explained that the region’s most iconic cultural products – windmills, Swedish meatballs, Danish pastries – have actually come from somewhere else.

“In a way, Scandinavia was brought here piece by piece,” the ad proclaimed, in a pitch to promote the benefits of travel. It received a rain of complaints and attacks in what appeared to be a coordinated harassment effort and included a hoax bomb threat.

That came just after a furore over the BBC children’s TV series Horrible Histories. A special episode marking Britain’s exit from the EU included a song called “British Things”, which discussed the origin of products such as sugar, tea and the nation’s royal family. It was slammed as “anti-British” by critics, including prominent historians, some of whom railed against an inferred suggestion that Britain had failed to produce anything of note.

These perceived slights against national culture and identity are recurring themes – and Britain has plenty of them. Actor Laurence Fox drew criticism – and later apologised – when he referred to “the oddness in the casting” of a Sikh soldier in a British regiment in the film 1917. The film depicts events of the first world war, in which up to 130,000 Sikh men took part, forming 20 per cent of the British Indian army.

In 2017 a BBC cartoon depicting life in Roman Britain, which featured a black Roman general, set off a row over that period’s ethnic diversity. The historian Mary Beard suffered a torrent of social media abuse for noting that the cartoon was “pretty accurate”. Meanwhile, who could forget the Conservative MP who lambasted the London 2012 Olympics’ opening ceremony as “leftie multicultural crap” (he later apologised). Or the outrage in 2018 over the discovery that Cheddar man, the first modern Briton who lived around 10,000 years ago, may have been black.

Such rows keep recurring because of the relentless tug of a nativist portrayal of identity. At its core, the narrative – a favourite of the populist right – holds that there existed a time when a nation and its cultural output were great, and that this epochal time was before migrants turned up. Any suggestion that diversity is embedded throughout history and has created cherished cultural icons explodes that theory. After all, if you are nostalgic about a time when Britain was less multicultural and also better, which period do you mean? As the row about diversity in Roman Britain revealed, you’d have to go a long way back in history.

This enduring myth about British identity is described by Sivamohan Valluvan in his book The Clamour of Nationalism: Race and Nation in Twenty-first Century Britain as the “entrenched memory of its history as being an unbroken succession of whiteness”.

Such assumptions permeate the way politicians and commentators of all stripes often talk about immigration. This issue is framed in anxieties over the “pace of change” and “cultural concerns” – as though a static and default culture is being disrupted, rather than simply continuing along its usual and historic course. This theory seems to persist regardless of the number of times Britain is identified as a migrant nation, or how often we note the contributions to quintessential British life brought by each wave of immigration: Romans, Anglo-Saxons, Celts, Vikings, Normans, Roma, Huguenots, Africans, Jews, Indians and many others.

Meanwhile, the refusal to reconcile with Britain’s hybridity is stamped all over the government’s immigration proposals.

Now migrants are to be ranked according to economic benefit using a points system, which cannot possibly score the immeasurable ways in which people arriving from other countries have already improved this one. How do you explain to someone with a nativist mindset that diversity is what makes nations thrive, that exposure to difference is what brings unpredictable spurts of progress, unimagined creativity and untold innovative leaps? A cursory glance over the past few years alone would produce examples including the Nobel-prize winning material graphene, award-bagging big data projects and field-leading components that power up wind turbines. You could talk about education and learning, literature, theatre, fashion, architecture and music. You could go on and on.