Students in Tehran have thrown stones and petrol bombs at the British embassy in protest at international pressure over Iran's nuclear programme.
Riot police clashed with protesters after the rally turned violent
The protesters called for the expulsion of the ambassador and urged a repeat of the US embassy hostage-taking of 1979.
Britain helped draw up a resolution at the UN nuclear agency agreeing to report Iran to the Security Council for breaking its nuclear commitments.
Police with batons broke up the protest and some demonstrators were injured.
Several windows were broken by stone-throwers but there are no reports of injuries inside the embassy.
The protest - organised by the hardline Islamist Student Basij Organisation - started off peacefully.
Protesters chanted slogans calling for a repeat of 1979 when revolutionary students stormed the US embassy and took hostages.
Suddenly tomatoes, rocks and firecrackers were thrown at the embassy gate, followed by Molotov cocktails.
Chants of "Nuclear energy is our legitimate right" turned more violent, with protestors shouting "marg bar ingelis" - "death to England."
One protester whose forehead was cut by a police baton left bloody hand-prints on a brass plate on the embassy wall.
Correspondents say that the British mission bares the brunt of anti-Western demonstrations in Tehran because the US does not have a diplomatic presence there.
Earlier in the day UK Foreign Secretary Jack Straw told the BBC he believed military action against Iran was inconceivable, despite US statements that every option remained open.