Dozens of hard-liners gathered in front of the embassy compound following Friday prayers in the Iranian capital holding up signature-yellow flags of the Lebanese militia Hezbollah.
They threw stones at the embassy building, shattering several windows, and tore down the embassy plaque on the gates of the compound.
Several British flags were set on fire during the demonstration.
They were protesting what they said was British support for the Israeli offensive against Hezbollah forces in Lebanon.
The group also chanted slogans against several international human rights organisations, accusing them of failing to oppose the violence in Lebanon.
