DAVID Cameron last night branded the Iranian government a “disgrace” for failing to protect the British embassy and its staff from surging protesters.

The Prime Minister, who chaired a meeting of the Cobra security committee after details of the assault on two compounds emerged this afternoon, demanded the attackers faced prosecution.

Echoing Foreign Secretary William Hague’s warning that there would be “serious consequences” for the breach of international law, Mr Cameron said the Government will consider what measures to take in the next few days.

He said: “The attack on the British Embassy in Tehran today was outrageous and indefensible. The failure of the Iranian government to defend British staff and property was a disgrace.

“Our immediate priority is the safety of our staff. I spoke to our ambassador this afternoon and was reassured that everyone has been accounted for.

“He and his team have handled a dangerous situation with calm and professionalism. We hold the Iranian government responsible for its unacceptable failure to protect diplomats in line with international law.

“The Iranian government must immediately ensure the continued safety of our staff, return all property and secure the compound immediately.

“Those responsible for this criminal attack must be prosecuted.

“The Iranian government must recognise that there will be serious consequences for failing to protect our staff. We will consider what these measures should be in the coming days.”

Hundreds of protesters surged on two compounds yesterday afternoon, putting the safety of staff at risk and causing “extensive damage'' to property.

Mr Hague said Iranian police protected Britain’s ambassador and some staff earlier this afternoon from a large crowd outside.

He added: “There has been a confusing situation at times as to the whereabouts of certain staff. I wouldn’t use the term hostage. Clearly there have been situations where the Iranian police have intervened to try to ensure the safety of our staff.

“We are grateful for that but this situation should never have been allowed to arise in the first place.”

Mr Hague, who was told about the attack while he was in the Commons chamber listening to the Chancellor’s Autumn Statement, said Iran had “committed a grave breach” of the Vienna Convention, which demands protection of diplomats and diplomatic premises under all circumstances.

He added: “We hold the Iranian government responsible for its failure to take adequate measures to protect our embassy as it is required to do.

“I spoke to the Iranian foreign minister this afternoon to protest in the strongest terms about these events and to demand immediate steps to ensure the safety of our staff in both embassy compounds.

“While he said he was sorry for what had happened and that action would be taken in response, this remains a very serious failure by the Iranian government.

“The Iranian charge d’affaires has been summoned to the Foreign Office and the Prime Minister has chaired a meeting of Cobra.

“The safety of our staff is our utmost priority. On our latest information it now appears that all our staff and their dependants are accounted for. We are urgently establishing the whereabouts of our locally engaged security staff to ensure their wellbeing.”

British nationals have been warned against “all but essential travel” to Iran and the small number in the country were told to stay indoors and await advice.