Recent experience has shown that Tehran is the most adept at securing advantage from tensions between Iran and Britain, in spite of Iranian charges that it is the British who are masters of manipulation.
Tough words from David Miliband, the Foreign Secretary, were intended to defend the innocence of targeted embassy officials and ward off any further encroachment by Iran's hardliners. But they underlined that Britain has been only reactive throughout this saga. It withdrew diplomatic dependents only after pro-regime elements threatened to march on the embassy. Whitehall threw out two Iranian diplomats only after British officials were ejected from Iran. While it can complain about the arrest of its staff, there is nothing it can do about the detention of Iranian citizens in their own homeland.
Iran holds all the cards, and not for the first time. The revolutionary leaders have chosen to draw on ancient suspicions of British perfidy to consolidate their grip on power remarkably often.
Two years ago Iranian Revolutionary Guards seized a group of British sailors from Iraqi waters. It was clear that the junior members of a routine patrol allowed themselves to be taken without resistance because they understood the significance of an armed confrontation between Britain and Iran.
Iran, however, used the captured men and women to inflict humiliation on Britain. It held them in secret. It accused the group of spying. It highlighted the unpopularity of the British intervention in Iraq. It spurned any attempts to forge a diplomatic solution.
Then the regime staged a humiliating ceremony in the presidential palace in which the servicemen, by then dressed in shiny Chinese-made clothes, were handed presents by an exultant Mahmoud Ahmadinejad, the president of Iran recently re-elected in the controversial poll.
The shadow that hangs over this weekend's events is the 444-day hostage crisis in the American embassy in Tehran which started in 1979. In the run up to the taking of American hostages by revolutionaries, the embassy was vilified as a den of spies.
The sprawling British embassy compound in central Iran has formidable walls but could be similarly vulnerable. The rhetoric today is not identical to 1979, but accusing embassy employees of active involvement in a popular movement against the leadership comes uncomfortably close.
Meanwhile the two main theories to explain Iran's behaviour offer little prospect of restraint. The first says that Iran is diverting attention to Britain to preserve the prospect of talks with America. The second is that hardliners are deliberately upending relations with the West to sabotage any prospect of the thawing of relations voiced by Barack Obama, US president.
Either way, Britain finds itself with few options to arrest the downward spiral that Iran has initiated.
