The UK and other European nations must draw closer together as the US becomes a less-reliable partner, Keir Starmer has said in his first significant political intervention since leaving No 10.

The former prime minister warned European leaders of the threat posed by Russia, among others, and said the shift in relations with Washington during Donald Trump’s presidency was not likely to reset once he leaves the Oval Office. He accused them of being caught out by these new realities twice already.

“A stronger Europe is vital and the UK must be at the heart of it,” Starmer told an audience at the British Irish Chamber of Commerce on Friday. “Europe has twice been caught asleep, failing to anticipate and prepare for predictable events.

“First, when Russia’s attack on Ukraine exposed longstanding 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.…