I have been a proponent of engagement with Iran in the past -- but this kind of thuggishness and the failure of the Iranian security forces to protect the integrity of foreign embassies (again and again and again) underscores much of the reason why Iran is so very far away from being a nation in which others can have basic trust.
An attack on Iran leads to more nightmares than it solves -- but containment may be the only serious option left unless the more reasonable factions of Iran's political elite take over from a Supreme Leader who is undermining the interests and future of his country.
From Atlantic Wire's Adam Martin:
Students in Tehran stormed the British embassy there on Tuesday, forcing their way inside, where they threw papers from the windows and took down the British flag. The attack started with dozens protesting outside the building "to commemorate the death anniversary of Iranian nuclear scientist Majid Shahriari who, according to Iranian authorities, was murdered by Israeli's Mossad in cooperation with UK's MI6," Al Arabiya reports. The Times also reminds us that Iran had moved on Monday to downgrade diplomatic relations with Britain in retaliation for Western sanctions.
Here is a live blog and video of the Embassy attack.
Update: A good Reuters piece on factions inside Iran's government and how this Embassy incident further complicates nuclear negotiations.