The recent assault on the British Embassy in Tehran, which the Iranian authorities did nothing to stop until it was too late, led to the rupture of diplomatic relations between Britain and Iran. All British diplomats were withdrawn from Tehran and Iranian diplomats were expelled from London.
Under international law the Iranian government is obliged to take all appropriate steps to protect foreign diplomatic missions. Their failure to do so was a further example of Iranian contempt for their international obligations.
The ostensible reason for the assault was the British decision to apply sanctions against Iranian financial institutions. This followed a report from the International Atomic Energy Agency (IAEA) suggesting that Iran's nuclear program may have a military purpose. The United Nations has previously approved four rounds of international sanctions against Iran because of its failure to halt uranium enrichment and to cooperate with IAEA over its nuclear program.