British-flagged ships will be accompanied by a Royal Navy escort in the Strait of Hormuz amid growing tensions with Iran, the Government has announced.
Ships must hand in advanced notice of their plans so that frigate HMS Montrose can escort them.
It comes after the British-flagged tanker Stena Impero was seized by Iran's Revolutionary Guard on Friday.
The announcement in relation to Royal Navy escorts represents a change in policy.
On Friday, the Department for Transport advised ships planning to sail through the Strait of Hormuz to notify the UK authorities so they could, if necessary, arrange for them to travel in convoy.
The Government issued a new statement on Thursday which said: "Freedom of navigation is crucial for the global trading system and world economy, and we will do all we can to defend it.
"The Department for Transport has therefore updated its advice to confirm that the Royal Navy has been tasked to accompany British-flagged ships through the Strait of Hormuz, either individually or in groups, should sufficient notice be given of their passage."
Iran's president, Hassan Rouhani, suggested on Wednesday that Stena Impero could be released if the UK takes similar steps to hand back an Iranian oil tanker seized by the Royal Navy off Gibraltar earlier this month.
