ReutersBritish planes "are in the sky" in the Middle East "to protect our people, our interests and our allies," Prime Minister Sir Keir Starmer has said.
In a pre-recorded statement televised on Saturday afternoon, Starmer said protections for British bases and personnel had been stepped up to their highest level.
The US and Israel launched strikes across multiple Iranian cities including capital Tehran on Saturday morning, after negotiations to limit Iran's nuclear programme ended without an agreement. The UK did not participate in the strikes.
Earlier, the PM released a statement along with the leaders of France and Germany, calling for Iran to "refrain from indiscriminate military strikes".
In his speech, Sir Keir said he wanted to see "peace and security" in the Middle East and the "protection of civilian life".
He added: "Iran can end this now.
"They should refrain from further strikes, give up their weapons programme and cease the appalling violence and oppression of the Iranian people – who deserve the right to determine their own future."
Iran launched retaliatory attacks on Israel following the US-Israeli strikes, the Israeli military said, with explosions heard in several other countries in the region with US facilities.
The situation has caused disruption to air travel.
A Cobra meeting about the US and Israeli air strikes on Iran was held on Saturday morning, chaired by Sir Keir.
The emergency committee Cobra, which involves ministers and officials, meets to co-ordinate the government's response to an emerging situation.
"Iran must never be allowed to develop a nuclear weapon and that is why we have continually supported efforts to reach a negotiated solution," a government spokesperson said.
"Our immediate priority is the safety of UK nationals in the region and we will provide them with consular assistance."
They added: "We do not want to see further escalation into a wider regional conflict."
British people in Bahrain, Qatar, Kuwait and the United Arab Emirates have been told by the UK Foreign Office to immediately shelter in place following reports of missile attacks.
UK nationals in Jordan, Syria, Lebanon, Iraq, Yemen, Turkey, Saudi Arabia and Oman have been told to "remain vigilant" and take shelter if advised to do so.
Following the strikes on Iran early on Saturday morning, explosions and air raid sirens have already been heard in Qatar's capital, Doha, which is host to a US military facility. Qatar's defence ministry said it had intercepted Iranian missiles.
Bahraini state news is also reporting the service centre of the US Navy's 5th Fleet based in the Gulf nation had been "subjected to a missile attack".
Donald Trump has described the strikes as the start of "major combat operations" and called for Iranian government forces to lay down their arms.
The US president urged Iranians to shelter until the operation had finished.
Iran's Supreme National Security Council (SNSC) promised a "crushing" response to the US-Israeli attacks.
Many major airlines that serve the Middle East have diverted or cancelled flights over safety concerns.
British Airways has cancelled services to Tel Aviv and Bahrain until Wednesday, and Amman in Jordan on Saturday.
Virgin Atlantic said it cancelled a Heathrow to Dubai flight and warned that its flights to India, Saudi Arabia and the Maldives may take longer due as they had to be rerouted.
Wizz Air confirmed it has suspended all flights to and from Israel, Dubai, Abu Dhabi and Amman up until and including next Saturday.
Qatar Airways confirmed the temporary suspension of its flights to and from its capital Doha due to the closure of Qatari airspace, while Emirates said it was temporarily stopping services to and from Dubai.
Heathrow, the UK's busiest airport, urged travellers to check with their airline for updates.
Conservative leader Kemi Badenoch said she stood with the US and Israel "as they take on the threat of the Islamic Republic of Iran and its vile regime".
Meanwhile, Reform UK leader Nigel Farage said he prayed "for the right outcome for the wonderful Persian people" as "attacks against this evil regime in Iran begin".
Additional reporting by Matt Cole and Marc Ashdown
