Some of the staff at the UK's Iranian embassy have been withdrawn from Tehran following the storming of the building by protesters, the Foreign Office said.
Prime Minister David Cameron has warned the regime of Mahmoud Ahmadinejad of "serious consequences" following the attack, which saw hundreds of demonstrators smash windows, torch cars and burn Union flags.
The Prime Minister branded the Iranian government a "disgrace" for failing to protect staff at the embassy and two diplomatic compounds which were ransacked in the capital. Foreign Secretary William Hague is expected to update MPs on the situation in a statement to the House of Commons later on Wednesday.
Around 24 embassy staff and their dependants are based at the office and residential compounds in Tehran. The Foreign Office confirmed that a number of them were leaving the city in the wake of the trouble.
An FCO spokesman said: "The Prime Minister and Foreign Secretary have made clear that ensuring the safety of our staff and their families is our immediate priority. In light of yesterday's events and to ensure the ongoing safety, some staff are leaving Tehran."
Asked how many staff were leaving or if the embassy was going to remain open, he added: "We do not comment on our contingency plans and we will make any announcement about our embassy and staff at the appropriate time."
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. The attacks come two days after the Iranian parliament approved a bill reducing diplomatic relations with Britain following London's support of recently-upgraded US sanctions on Tehran.
The Bill - which marks a new low point in diplomatic tensions between London and Tehran - requires Iran and Britain to withdraw their ambassadors from each other's country and reduce representation to the level of charge d'affaires. It also calls for trade between the two countries to be reduced to "minimum levels".
Last week, the UK announced that it had severed all financial ties with Iranian banks in response to mounting fears over the country's nuclear ambitions. Chancellor George Osborne said all British credit and financial institutions had to cease trading with Iran's banks from the afternoon of Monday November 21 - the first use of the power to cut off an entire nation's banking sector.
The move was part of a wider international effort by the United States and Canada to put pressure on the Islamic republic, which western governments have accused of seeking to produce nuclear weapons for almost a decade.