The sprawling site near Sunderland of the giant Japanese car manufacturer Nissan is a fine-tuned product of Britain’s participation in the European Union. The company’s decision to pull the making of its proposed new X-Trail model out of that plant is a disastrous consequence of the failure to explain this to the British people.

The virtual absence of public explanation about the benefits of EU membership was exploited in the 2016 referendum by the leave campaign, and enabled its proponents to dismiss well-informed warnings, then and now, as scaremongering. Even on Sunday, when Nissan itself explained that Brexit uncertainty was a factor in its decision to build the new SUV in Japan, airtime was still given to Brexit campaigners denying this. Prominent among them, predictably, was Jacob Rees-Mogg, a backbench Conservative MP with no discernible car industry expertise or experience, whose Somerset constituency could hardly be further away from the north-east.

Theresa May made every effort not to publish assessments … which found that the north-east will be the worst-hit region

The alarm has been sounded before and since the referendum by Labour MPs in Sunderland, whose constituents work at a plant that has grown to employ almost 8,000 people and 30,000 more in the supply chain. Sharon Hodgson, the MP for Washington and Sunderland West, remembers the rush of optimism when Nissan arrived in the 80s, bringing hope to a region of closing mines and stalled shipbuilding. She is still trying to inform her leave-voting constituents about why Brexit chucks a spanner in the works.

Bridget Phillipson, the MP for neighbouring Houghton and Sunderland South, has argued that it is a dereliction of duty for Labour to acquiesce to Brexit knowing the economic damage it entails. After the weekend’s dire news from Nissan, she called again for a people’s vote with the option to stay in the EU.

Phillipson has lamented the gaps in public knowledge about the advantages conferred by EU membership, among remainers as well as leavers. But this is a blind spot with a long history. In fact, a prime example of a failure to inform the public, and instead mislead with propaganda, was a speech made by Margaret Thatcher when she opened the Nissan plant in 1986.

Thatcher had lobbied the Japanese government and industry since the 70s to set up in Britain; attracting their investment became a crucial component of her vision of Britain’s future, as she closed the old heavy industries down. Britain’s membership of the EEC was central to her sales pitch to the Japanese. The UK was presented as a convenient and agreeable base for the companies’ European operations. Nissan saw the business case for that, as have 1,000 other Japanese companies and other carmakers now using the UK as their European base.

Nissan chose the north-east principally for its ports, giving easy access to and from the European mainland. So Thatcher was fully aware that EEC membership was crucial to its decision to locate in Britain. In 1980, Keith Joseph, then a trade minister, wrote to her: “The deal [is] tangible evidence of the benefits to the UK of membership of the European Community; Nissan [has] chosen the United Kingdom because it [gives] them access to the whole European market. If we were outside the community, it is very unlikely that Nissan would have given the United Kingdom serious consideration as a base for this substantial investment.”

You will search in vain for a single word in the then prime minister’s speech that acknowledges that truth, however. She concealed the facts with a familiar comfort blanket – Britain’s supposed superiority to its European neighbours, which still echoes through the Brexit debate three decades on. Nissan’s decision, she said, was “confirmation … that within the whole of Europe, the United Kingdom was the most attractive country – politically and economically – for large-scale investment”.

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We can only speculate about how much more embedded public knowledge of the EU’s benefits would be today if she and other leading politicians had explained rather than obfuscated; if the basics had been taught in schools and reported honestly in the media. Attitudes might be very different if the EU flag had flown outside the Washington factory – and other sites of regeneration that owed their existence and success to Britain’s membership, and to substantial EU grants and loans over the years. Instead, the public has remained largely uninformed about the economic advantages of the EU and its “frictionless” single market, for which Thatcher herself pushed so hard.

Theresa May has engaged in similarly evasive public rhetoric since becoming the second Conservative female prime minister. In a speech made before the referendum, in which she backed remain, May said, “the economic arguments are clear”, and: “A lot of people will invest here in the UK because it is the UK in Europe.”

But since stepping over the fallen leadership candidates to become prime minister, May swerved into claiming Brexit is an economic opportunity. She made every effort not to publish her own government’s assessments of the economic damage Brexit would do, which found that the north-east would be the worst-hit region, with a 16% reduction in GDP in the event of a no deal, principally due to the impact on Nissan. Even since publication, she has barely mentioned these assessments, and has ploughed on instead, treating the 2016 vote as sacred.

To argue that the British public did not understand EU membership when fatefully asked to pronounce on it in a referendum is not to dismiss people as stupid. It is to recognise a decades-long failure of education and honest information, from the moment major companies such as Nissan came to Britain up to the point when, with their warnings about Brexit ignored, they began to withdraw.

• David Conn writes for the Guardian about sport, Brexit and other issues