William Hague warns Iran of international backlash
Mr Hague said the expulsion of Dominick Chilcott, who has been in Tehran just one month, would damage its ties with Europe and other Western states.
"If the Iranian government confirms its intention to act on this, we shall respond robustly in consultation with our international partners," Mr Hague said.
"It will do nothing to repair Iran's international reputation. To respond in this manner to pressure from the international community to engage is entirely counterproductive and yet another sign of Iran's continued unwillingness to enter into dialogue."
The Foreign Ofice was weighing its direct response, as the bill demands relations to be reduced to charge d'affair level but Iran does not have an ambassador in London.