Yvette Cooper is set to warn that any move by Iran to impose tolls on ships passing through the Strait of Hormuz would create a dangerous precedent for global shipping lanes. During talks in Tokyo with Japanese foreign minister Toshimitsu Motegi, she will stress the importance of reopening the vital waterway, through which roughly one fifth of the world’s oil supply normally passes.

Iran closed the strait following air strikes by the United States and Israel, prompting President Donald Trump to launch a blockade of Iranian oil ports. Tehran has said vessels may transit the strait only in coordination with Iranian authorities and if they pay a toll, while insisting access will remain restricted as long as the United States blockade continues.

The diplomatic push comes ahead of the expiration of a ceasefire between Washington and Tehran. Trump has announced further negotiations in Pakistan and warned of severe consequences if Iran rejects a deal, while accusing Tehran of breaching the truce.

Meanwhile, Prime Minister Keir Starmer and French President Emmanuel Macron have led discussions in Paris on safeguarding maritime traffic. Starmer said the United Kingdom and France would spearhead a peaceful mission to protect freedom of navigation once conditions allow, amid criticism from Trump that European allies had been ineffective during the crisis.