All Iranian diplomats left Britain on Friday, expelled by the British government in response to protesters storming its embassy in Tehran, hardening a confrontation between Tehran and the West over its nuclear programme.

I can confirm that, earlier this afternoon, all diplomatic staff of the Iranian Embassy in London took off from Heathrow airport, a Foreign Office spokesman said.

Foreign Secretary William Hague announced on Wednesday that Britain was closing its embassy in Tehran, a day after protesters stormed two British diplomatic compounds there, smashing windows, torching a car and burning the British flag in protest against new sanctions imposed by London.

Hague said the assault could not have happened without the consent of Iranian authorities and ordered the closure of the Iranian embassy in London and gave all Iranian diplomats 48 hours to leave Britain.

The move sent relations between Britain and Iran plunging to their lowest level since Iran broke diplomatic relations with Britain in 1989 over Salman Rushdie's novel The Satanic Verses which Iran's then leader said blasphemed against Islam.

The Iranian diplomats slipped away quietly. The green, white and red Iranian flag still flew over the Iranian embassy in west London that was the scene of a dramatic six-day siege in 1980 when gunmen seized 21 hostages, two of whom they killed.

Across the street, a dozen protesters opposed to Iran's government chanted Free Iran and urged terrorists to go home. A few police officers stood guard.

This week's spat exacerbates a standoff between Iran and the West over Iran's nuclear programme at a time when there has been renewed speculation that Israel or the United States could launch military strikes against Iran's nuclear infrastructure.

Western powers suspect Iran is seeking to develop nuclear weapons but Iran insists its programme is peaceful.

REMORSE

Britain's Ambassador to Iran, Dominick Chilcott, said hardliners in the Iranian establishment may have thought confrontation would rally Iranians to their cause but miscalculated how strong Britain's response would be.

They probably didn't expect us to send home the Iranian embassy in London and, reading between the lines, you can see in the way they have responded to that move, some remorse in having provoked it, Chilcott told the BBC.

Analysts said the closure of the embassies, by cutting off a channel of communication between Britain and Iran, complicates the search for a diplomatic solution to the nuclear dispute.

Having this tension between Iran and Europe will make those negotiations a lot harder, said Adam Hug, policy director of the Foreign Policy Centre, a London think-tank.

It does make the risk of conflict slightly more plausible, he told Reuters.

France, Germany and the Netherlands recalled their ambassadors from Tehran for consultations as a protest against the storming of the British embassy compounds and the European Union moved swiftly to ratchet up sanctions.

The EU added 180 Iranian people and entities to its sanctions list on Thursday and laid out plans for a possible embargo on Iranian oil, the lifeblood of the Iranian economy.

Former Foreign Secretary David Miliband, of the opposition Labour Party, warned in an article in the Financial Times on Friday that growing talk of a military option in Iran risked creating a logic of its own.

A concerted diplomatic effort on Iran is needed now to prevent the world sleepwalking into another war in the Middle East, he said.

(Additional reporting by Toby Melville and Stefano Ambrogi; Editing by Jon Hemming)