TEHRAN // Iran's Guardians Council approved a parliamentary bill demanding Britain's ambassador to Tehran be expelled within two weeks, making it law, state television's website reported.
The confirmation by the council means Iran's foreign ministry now has to apply the measure.
Britain has threatened to act "robustly" if the expulsion is carried out.
Iranian legislators on Sunday passed the bill in retaliation for fresh western sanctions over Tehran's nuclear programme, in particular Britain's announcement it was "ceasing all contact" between its financial system and that of Iran.
The law calls for diplomatic ties between Iran and Britain to be downgraded to the more junior charge d'affaires level, and for trade and financial ties to be reduced to a minimum.
It also contains a clause warning that other countries could also be punished if they followed Britain's lead.
"After discussions, members of the Guardians Council have passed the law unanimously," the Guardians Council spokesman, Abbas Ali Kadkhodaei, said.
Britain unveiled its new sanctions on Iran on November 14, in conjunction with similar measures by the United States and Canada.
They based their step on a report by the UN atomic energy watchdog a week earlier that strongly suggested Tehran was researching nuclear weapons.