A British-flagged tanker was seized by Iranian forces last week (Picture: US Navy).
The Royal Navy will escort British-flagged vessels travelling through the Strait of Hormuz.
The Government said the move was in response to the "heightened threat to commercial shipping in the Gulf".
Tensions in the region have escalated over the past month, including an incident where a British-flagged tanker was seized by Iranian forces.
Watch: HMS Montrose escorts two tankers through the Strait of Hormuz
A Government spokesperson 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."
The seizing of the British-flagged Stena Impero came after UK forces seized an Iranian oil tanker near Gibraltar.
The tanker seized by British forces was allegedly heading for Syria and going against European Union sanctions.
The UK wants to create a European-led maritime protection mission to ensure safe shipping in the Gulf.
France, Italy and Denmark support the idea, three EU diplomats said on Tuesday, while Germany says is too early to discuss the proposal.