HMS Duncan has joined frigate HMS Montrose to escort vessels sailing under the British flag through the Strait of Hormuz.
HMS Montrose has so far accompanied 35 vessels through the strait, according to the Ministry of Defence (MoD).
Defence Secretary Ben Wallace said the UK continued to push for a diplomatic resolution to the situation.
He said: "Freedom of navigation in the Strait of Hormuz is vital not just to the UK, but also our international partners and allies.
"Merchant ships must be free to travel lawfully and trade safely, anywhere in the world."
Mr Wallace added the Royal Navy will continue to provide a safeguard for UK vessels "until this is the reality".
HMS Duncan is a Type 45 Destroyer which the Royal Navy describes as "among the most advanced warships ever built".
Why have tensions escalated?
Earlier this month, British Royal Marines helped seize Iranian tanker Grace 1near Gibraltar which was suspected of breaking EU sanctions, infuriating Iran.
In response, Tehran threatened to capture a British oil tanker.
On 19 July, British-flagged oil tanker Stena Impero was seized by Iran's Revolutionary Guard in the key shipping route.
A second British-linked tanker, the MV Mesdar, was also boarded by armed guards but was released.
Tehran said the Stena Impero was "violating international maritime rules".
HMS Montrose was alerted but it was too far away to stop the seizure.
Iran's state-run IRNA news agency said the tanker was captured after it collided with a fishing boat and failed to respond to calls from the smaller craft.
But the then foreign secretary Jeremy Hunt said it was seized in Omani waters in "clear contravention of international law" and then forced to sail into Iran.
The tanker's Swedish owners, Stena Bulk, said it had been complying with regulations and had been in international waters.
Stena Bulk said the 23 crew members, who are Indian, Russian, Latvian and Filipino, are in good health and have met with officials from their respective countries.
BBC
