Sir Keir Starmer has arrived in Saudi Arabia as he visits Gulf allies to push for a long-term resolution to the Iran conflict.
It comes after Iran and the US agreed to a two-week ceasefire on the condition that Iran reopens the Strait of Hormuz for shipping.
The Prime Minister is set to hold talks with Gulf leaders including Saudi Arabia’s Mohammed bin Salman on how best to support the pause in fighting and ensure passage is permanently restored through the key oil and gas shipping route.
Sir Keir is also expected to thank armed forces from the UK and allied countries who are posted in the region.
The ceasefire announcement triggered a fall in global oil prices and an upswing in stock markets as investors breathed a sigh of relief following weeks of economic turmoil.
On Wednesday morning, London’s FTSE 100 index of major firms jumped by as much as 2.6% at the start of trading on the back of the deal.
The price of benchmark Brent crude oil slid by 14.3% to 93.6 US dollars (£69.78) a barrel, although this was still well above the price of around 70 dollars at the start of the conflict.
The US-Israeli strikes on Iran and Tehran’s response, including targeting Gulf states and effectively closing the Strait of Hormuz, had sent fossil fuel prices soaring around the world.
Petrol and diesel costs for motorists in the UK have risen sharply since Donald Trump launched his military action.
The average price of diesel was 190.6p on Wednesday morning, up 34% since February 28 when the US-Israeli action began, motoring organisation the RAC said, while average unleaded prices reached 157.7p, up 19%.
Mr Trump had threatened to obliterate Iran’s power plants and bridges if a deal could not be reached to reopen the Strait of Hormuz.
But less than two hours before his deadline expired the US president said he was suspending his threat.
A joint statement by world leaders including Sir Keir said they would “contribute to ensuring freedom of navigation in the Strait of Hormuz”.
The statement, signed by the leaders of the UK, France, Italy, Germany, Canada, Denmark, the Netherlands, Spain and the presidents of the European Commission and European Council, welcomed the ceasefire.
“We strongly encourage quick progress towards a substantive negotiated settlement,” they said.
“This will be crucial to protect the civilian population of Iran and ensure security in the region.
“It can avert a severe global energy crisis.
“We support these diplomatic efforts.
“To this end, we are in close contact with the United States and other partners.
“We call upon all sides to implement the ceasefire, including in Lebanon.”
Israel maintained its attacks on Lebanon, the base for Iran-backed Hezbollah, claiming it was not covered by the ceasefire deal.
The ceasefire deal has resulted in what US vice president JD Vance called a “fragile truce”, with reports from the Gulf of missile or drone raids on Kuwait and the United Arab Emirates while Iran claimed its Lavan Island oil refinery had come under attack.
Announcing the two-week pause in the bombing campaign, Mr Trump said Tehran proposed a 10-point plan that provided “a workable basis on which to negotiate”.
But he warned US forces would be “hangin’ around in order to make sure that everything goes well”.
Tehran wants the deal to keep the strait under Iranian control, allowing it to levy tolls on shipping.
Pakistan prime minister Shehbaz Sharif said he had invited Iranian and US officials to Islamabad for talks on Friday.
Mr Trump wrote on his Truth Social platform: “We received a 10 point proposal from Iran, and believe it is a workable basis on which to negotiate.”
He said it was “a big day for World Peace!” and predicted “the Golden Age of the Middle East”.
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