Keir Starmer used his first significant political intervention since leaving Downing Street to tell European leaders that the continent can no longer count on the United States to pay for its security, and that the change will outlast Donald Trump's presidency.

Speaking at a British Irish Chamber of Commerce dinner in Dublin City Hall on Friday evening, the former prime minister said the UK and its neighbours had been caught unprepared twice: by Russia's full-scale attack on Ukraine, and by Washington's decision that it would no longer "bankroll" European defence.

"Europe has twice been caught asleep – failing to anticipate and prepare for predictable events," he said. "First when Russia's attack on Ukraine exposed long-standing European weaknesses on defence and security; and second when President Trump made clear, once and for all, that the US will no longer bankroll our European security. We have to catch up."

A permanent shift, not an aberration

Starmer was blunt about the durability of the change. "This is about responding to a permanent change of affairs, not an aberration of the Trump presidency," he said. "Things will not go back to the way they were before."

That argument matters because much of European planning has rested on the assumption that a future American administration would restore the old arrangement. Starmer, who left office in July, said the shift in dealings with Washington was not likely to reset once Trump leaves the Oval Office.

The relationship has been uneven. The pair developed a positive relationship in their opening months of working together, which Starmer's team highlighted at the time as one of the biggest successes of his premiership. But Trump later mocked him as being "no Winston Churchill" in a row over the refusal to permit the use of UK bases for the initial US-Israel strikes on Iran. Starmer said in July that he would "keep in touch" with the president after his time in Downing Street ended.

He was careful to say the diagnosis was not a break with the US. His comments did not mean "the US relationship is no longer important", he said. "On the contrary, the military, security and intelligence alliance is far too strong for that. But it does mean enabling Europe to take on far more responsibility for its own defence and security."

A common security framework

The former prime minister's prescription went beyond spending targets. "A stronger Europe is vital and the UK must be at the heart of it," he said, arguing that a "common security framework" for Europe was needed as much as a common market.

"We need to build up pan-European co-operation and co-ordination on defence and security – a common security framework as much as a common market," he told the dinner, where he was awarded an honorary life membership of the chamber.

He said the EU was already changing in response, but warned that the effort "cannot be the EU alone when Europe's periphery is core to its defence" — a line that puts Britain, outside the bloc since Brexit, inside the argument about how European defence is organised.

The domestic argument

Starmer has made closer European ties his cause since before leaving office. Three months before he stepped down, amid Trump's war with Iran and his threats to withdraw from Nato, he described Europe as a "partnership for a dangerous world we must navigate together". He said then that the relationship should go further than defence, arguing that Brexit had done "deep damage" to the UK economy and that he wanted "closer economic cooperation [and] closer security cooperation".

His Dublin visit included meetings with senior business leaders and politicians, among them the taoiseach, Micheál Martin, with whom he established an annual UK-Ireland summit.

The political weather in London has moved his way. Soon after taking office as his successor, Andy Burnham said he intended to be "bolder" about closer ties with the EU. Starmer's remarks reflect a growing consensus on the left of British politics that closer ties with Europe are essential to economic and military security.

A warning dressed as a lecture

The speech was framed as a warning rather than a farewell. Europe's rearmament is already under way — Nato allies have signed up to a new 5% defence spending pledge that Trump has called a "big win", and Washington this week approved a further Patriot interceptor sale to Ukraine — but Starmer's point was that money alone will not close the gap.

His two examples were chosen to show that the continent's problem is anticipation, not resources. The Russian attack exposed long-standing weaknesses, and the American pivot exposed the assumption underneath them. "We have to catch up," he said.

Britain must be central to the project, Starmer argued, because of what it brings. "We are one of two nuclear powers. We are a leading Nato member. We have a viable next-generation fighter jet programme. And we are pledged to work alongside European allies to guarantee security in Ukraine," he said.

He spoke as the defence secretary, Wes Streeting, told a meeting of European defence ministers in Paris this week that they were "united and unwavering" in support for Ukraine in the face of Russian hostility.

For a former prime minister who spent his final months in office arguing for closer European ties, the Dublin speech is a marker of how quickly that argument has become mainstream — and of how little time he thinks Europe has to act on it.