Diplomats based at the Iranian embassy in London are preparing to leave Britain.
They were given a deadline of Friday afternoon by the UK Government after being expelled following an attack on the British Embassy in Tehran.
Meanwhile, Europe stepped up economic and diplomatic sanctions against Iran.
At talks with fellow EU foreign ministers on Thursday, Foreign Secretary William Hague welcomed what he described as "a great deal of solidarity" from other EU capitals over the attack, with many countries withdrawing their ambassadors from Iran in protest.
But he said another round of sanctions designed to further isolate the regime was a separate issue already on the EU agenda.
The new sanctions include adding 180 individuals and Iranian businesses associated with the regime to a list of those banned from travel in Europe and whose European assets are frozen. They were people and companies involved with Iranian shipping lines, financial services, energy and transport, or those associated with the Iranian Revolutionary Guard.
Mr Hague said further work on economic sanctions would continue towards a possible ban on Iranian oil exports to the EU:
"We have agreed to do further work to be brought forward to the next meeting of foreign ministers in January, but it is too early to say we have agreed to any oil measures," said Mr Hague. He added: "There will be further measures against Iran unless Iran changes its behaviour and the course of its (nuclear) policies."
Mr Hague said the UK was pleased with the outcome, but it was not the end of the issue - further measures to be discussed next month would be designed to "severely affect the Iranian financial system and the energy and transport sectors".
A ban on Iran exporting its oil to the EU could hit European companies and worsen the economies of some struggling member states which might face higher prices for oil from elsewhere.