Britain faces further isolation after Brexit if it doesn’t adjust its citizens’ attitude towards learning foreign languages, a panel of experts has warned, with Britons becoming increasingly “linguaphobic” in the wake of the EU referendum.

Speaking at the Hay literary festival on Friday, a panel including Cardiff University professor Claire Gorrara and linguist Teresa Tinsley, said that Britons had too long relied on a false belief that English was the world’s lingua franca. Only 6% of the global population are native English speakers, with 75% of the world unable to speak English at all. But three-quarters of UK residents can only speak English.

“That English is somehow the norm is a complete misapprehension of the facts, but this notion that everyone is speaking English is persistent and believed by many in the UK,” said Gorrara, warning that economic opportunities and bridge-building with the rest of the world was at risk after Brexit if Britons did not become less “linguaphobic” and learn more languages.

Deficient language skills in the UK cost 3.5% of GDP, according to 2014 research by Cardiff Business School for UK Trade and Investment. A 2017 British Council report recommended that the top five languages needed by the UK “for prosperity and influence” post-Brexit are Spanish, Mandarin Chinese, French, Arabic and German.

The same report also found that there was a “growing language deficit” in the UK, which is expected only to grow post-Brexit because the UK’s £1bn “language industry” – including services such as translation and interpreting – already heavily relies on EU citizens, whose expertise may become harder to access.

Speaking at Hay, Tinsley said that in forthcoming research commissioned by the British Council, due to be published next month, a survey of around 700 modern-language teachers in England found that a third felt Brexit had resulted in a negative attitude towards learning foreign languages in their school, among both parents and pupils.

Tinsley, who worked on the report, said these respondents tended to work in England’s most deprived areas.

“Brexit was the biggest impact that we saw in the state sector [on attitudes to learning languages],” she said. “I don’t know if it has to do with the general sense of isolationism or anti-immigrant or anti-foreigner feeling, or perhaps a mistaken idea of what’s going to happen when we leave the European Union, that we won’t need to speak other languages any more.”

However, she said that the referendum result had also galvanised a reverse response in some schools, with those language teachers reporting an increased sense of need for their subject after the 2016 Brexit vote.

With 94% of language students in Europe learning English and 51% studying two or more foreign languages, the UK has long lagged behind the European Union linguistically. After 2004, when languages became optional for UK students once they turned 14, GCSE take-up halved, going from nearly 80% to around half that in 2017. Applications to study modern foreign languages at university have also dropped 57% in the last decade.