THE official notification, delivered in secure calls yesterday morning to senior Whitehall figures, was the latest dramatic behind-the-scenes move to get to grips with a crisis that is now engulfing the government.
After a day of shadow-boxing with a notoriously slippery regime, Tony Blair is set to up the ante: the plight of the Shatt al-Arab 15 is officially a crisis and he will need the Cobra team to handle it.
The clutch of VIPs will gather in an operations room several floors below Downing Street as early as this afternoon to plot an escape from a military spat that now threatens to become an international incident.
The decision came just 24 hours after the crew of HMS Cornwall had been caught in the confusion of direct confrontation with Iranian vessels in the searing heat of the Gulf.
As the crew members were surrounded in their two rubber dinghies, the Cornwall's commander, Commodore Nick Lambert, frantically radioed back to his own top brass for instructions.
The response to the inquiry, which had been immediately patched through to Ministry of Defence headquarters in Whitehall, was to hold fire.
The order to show restraint has been observed throughout the forces and the British government in the 48 hours since, but it is unclear how long both sides will be able to maintain control.
Foreign Secretary Margaret Beckett's first response to the gathering crisis on Friday was to keep to diplomatic conventions. After a hurried phone call to Blair, she immediately summoned Iran's ambassador, Rasoul Movahedian, to her office to explain their behaviour.
After a meeting described by officials as "brisk but polite", Beckett emerged to stress that she was "extremely disturbed" by events.
It was an understated description of the deep concern now gripping the government. Not only was Blair's administration alarmed at the risk to the 15 military personnel, which included at least one woman, but it was in no doubt over Tehran's ability to use their plight to make a wider point.
During a flurry of diplomatic activity in the hours after the snatch, the Iranians' rhetoric repeatedly elevated their action, and the alleged motives of the British, to a multinational affair. It was the eve of a second UN Security Council resolution imposing sanctions over Iran's refusal to halt its programme to enrich uranium. The Shatt al-Arab 15 were, from the start, pawns in a perilous international game.
"It looks like too much of a coincidence," a senior Foreign Office insider confirmed.
The response was a no- nonsense demand for Iran to relent - and Britain freely used the international community to back up its case. Beckett dispatched the UK charg d'affaires, Kate Smith, to confront the government in Tehran, armed with the insistence that the British sailors had been in Iraqi waters.
In the meantime, Blair made a personal call to European allies, including EU foreign policy chief Javier Solana, to secure a public denunciation of the Iranians' actions.
"It was impressed on everyone how important it was to raise the diplomatic temperature, rather than keep a low profile and let them make a song and dance of the situation," one defence official said.
"There is nothing to be gained in provoking a confrontation, because that would be playing into their hands. But neither should we let them have it all their way. We tried that before and we're still trying to get our kit back."
The smaller-scale precedent, the taking of six British marines and two sailors on the same waterway in June 2004, was a painful lesson. The personnel were only returned after they had been paraded blindfold on Iranian television and admitted entering Iranian waters illegally. Three years on, the government is still pressing Iran for the return of its boats and kit, including valuable radar equipment.
The degree of concern felt across Whitehall was demonstrated yesterday, when Movahedian was called back to the Foreign Office, this time to see Beckett's minister, Lord Triesman. The British were clearly attempting to warn off Tehran before it could begin to use the servicemen and women as a significant propaganda tool.
It was, however, a race against time - and through it all, the diplomats and the politicians were acutely aware that Tehran has built a foreign policy on disregarding diplomatic niceties.
COBRA is an acronym for Cabinet Office Briefing Room A, where its meetings are held.
Tony Blair, senior ministers, police and security chiefs all take part. It is called after events such as 9/11, 7/7
and can evoke emergency powers such as suspending Parliament or restricting movement.