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 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.
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