But in a video address posted to social media, he added: "We were not involved in the initial strikes on Iran, and we will not join offensive action now.

"But Iran is pursuing a scorched-earth strategy, so we are supporting the collective self-defense of our allies and our people in the region."

United Kingdom (UK) UK foreign office to review pay-off to Epstein-linked US envoy Peter Mandelson

Starmer added: "Our decision that the UK would not be involved with the strikes on Iran was deliberate.

"Not least because we believe that the best way forward for the region and for the world is a negotiated settlement."

A separate statement posted on the UK government website set out its legal position.

Earlier Sunday, France, Germany and the UK said in a joint statement they were ready to defend their interests and those of its allies in the Gulf if necessary by taking "defensive action" against Iran.