Donald Trump’s contorted spin on the travel restrictions he announced on Wednesday night, including pinning the blame for “a foreign disease” on the European Union, revealed a mind largely driven by politics and not science.

The impression he sought to create was that the EU bureaucracy had let the world down by failing to take necessary steps to slow the spread of coronavirus, but the United Kingdom, legally outside the EU and physically an island, was exonerated.

“We will be suspending all travel from Europe to the United States for the next 30 days,” the president said, specifically adding that these restrictions would not apply to the UK, without mentioning any other exemptions.

Trump’s greatest friend in the UK, Nigel Farage, applauded the drastic but necessary measures. “The UK is now being treated as an independent country,” he tweeted. The rewards of Brexit were already being reaped, in what looked like a big win for British diplomacy and the special relationship.

But the reality, once the true details of the Presidential Proclamation were released, was somewhat different.

The White House briefing paper said the US was closing its borders to foreign nationals who have been in the Schengen area in the last 14 days, which would apply to any British person who had recently been in the 26-nation visa-free area.

Five other EU countries were also excluded from the US travel ban. So if the announcement was a big win for London’s diplomatic heft, the same could be said of Bucharest, Nicosia, Zagreb, Dublin and Sofia, the capitals of five EU countries outside Schengen.

The reality is that no European diplomat, including in the UK foreign office, had been forewarned that Trump, after a week of mishandling the crisis, was to put the EU in the dock in a bid to try to reinsert himself at the helm of the crisis.

Many explanations have been offered for why Trump presented his announcement as he did. His prejudice against the EU is well known, and targeting Schengen countries gave him a chance to exempt the US’s natural allies Ireland and the UK.

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It may be that Trump has never heard of Schengen, Luxembourg or the Schengen free travel area. His spinners thought, rather than bamboozle an American public, and possibly the president, with the complexities of EU border areas, the neater impression should be left that the EU and not Brexit Britain was being targeted.

An alternative explanation is that Trump had only cursorily acquainted himself with his own announcement, and misspoke. Elsewhere in his statement he twice said that goods from Europe would also be banned, a mistake that was hastily “walked back” by his briefers.

It may also be that the White House itself was not very convinced at the rationale of picking on the Schengen area for exclusion. The official explanation was the Schengen area had the largest number of coronavirus cases outside China. As of 12 March, the White House said the number of cases in the 26 Schengen countries was 17,442, with 711 deaths, and showed high continuous growth in infection areas. In total, Schengen countries had exported 201 cases to 53 countries.

Moreover, the free flow of people between the Schengen countries made the task of preventing the coronavirus from spreading difficult, the White House said.

This ignored the large number of cases in the UK, the lack of virus testing in the US and the fact that some Schengen area countries, such as Poland and Denmark, had already effectively closed their borders to EU citizens.

Ironically, the announcement represents a headache for the UK as its transport officials try to work out whether it will become a transit hub for Europeans seeking to reach the US.

Trump, after a week as a bystander, has put his imprimatur on the coronavirus crisis, and in a way that hammers UK shares. Larry Summers, the former chief economist at the World Bank, commented: “The president has set what I believe is a new world record for presidential market value destruction. He destroys about $500bn in equity market value in course of an 11-minute speech. Destruction roughly doubles as investors take an hour to analyse the speech. Loose lips sink ships. Imprudent rhetoric sinks markets.”

Trump has form on politically motivated but arbitrary travel bans, notably on Muslims. In January 2017 he barred people from seven majority-Muslim countries – Iran, Iraq, Syria, Yemen, Somalia, Sudan and Libya – from entering the US for 90 days. The travel ban was later struck down as unconstitutional by the courts on the grounds that there was no rationale to have a ban that put religion at its heart. But this did not stop him from using the threat of a ban as a bargaining chip with Gulf states.

In this latest ban, the guiding principle may not be religion, but animus towards an institution that challenges nationalism. Either way, the decision, and the manner in which it was taken, has left even British politicians appalled. Tom Tugendhat, the chair of the UK foreign affairs select committee, warned: “How countries work together in moments of crisis will shape how we cooperate after. This is a moment for the UK to reach out around the world to allies and friends to help coordinate action and support.”

The implicit criticism is that the US is not at present able to fulfil that role.