IRAN-backed terror cells could be deployed to launch deadly attacks in the UK, according to intelligence sources quoted last night.

As tensions escalate over the seizure of a British oil tanker, spy chiefs believe Iran may give the green light to its hidden proxy fighters if the crisis deepens.

Among senior intelligence officers, Iran ranks behind only Russia and China as the nation state posing the greatest threat to Britain’s national security and the seizure of the UK-flagged oil tanker Stena Impero will have intensified concerns in MI5 and MI6.

Intelligence agencies believe Iran has organised and funded sleeper terror cells across Europe including the UK and could greenlight attacks in response to a conflict in the Gulf.

Office, local government and private sector emails at the end of last year.

The Department of Transport have claimed the Steno Impero was in Omani waters when it was seized before being re-routed by Revolutionary Guard special forces and produced naval charts to support this claim.

The British Government described the incident, a response to the seizure of Panamanian flagged Grace I in Gibraltar, as “illegal” and wrote in a letter to the UN Security Council: "Current tensions are extremely concerning, and our priority is to de-escalate. We do not seek confrontation with Iran. But it is unacceptable and highly escalatory to threaten shipping going about its legitimate business through internationally recognised transit corridors."

The Saudi Foreign Affairs Minister Adel Aljubeir tweeted last night: "Iran must realise that its acts of intercepting ships, including most recently the British ship, are completely unacceptable. The world community must take actions to deter such behaviour."