The foreign secretary will call for the Strait of Hormuz to be fully reopened later on Thursday after ships in the Gulf were warned by the Iranian navy that those without permission to pass through faced attack.
In her annual speech on UK foreign policy priorities, Yvette Cooper will also call for Lebanon to be included in the US and Israel's ceasefire agreement with Iran.
Cooper will add there cannot "be any place for tolls on an international waterway" as ships face uncertainty on possibly making payments to Iran to secure safe passage.
Sir Keir Starmer is visiting allies in the Gulf, last night meeting Saudi Crown Prince Mohammed bin Salman, who agreed on the need for a lasting peace.
This evening, Cooper is expected to say that the war has affected "every country on every continent", driving up food and petrol prices in the UK.
