Today's dramatic anti-terror developments have led to the convening of the Government's "Cobra" emergency response committee.
Home Secretary John Reid said he had chaired two Cobra meetings of senior officials, police and security service personnel overnight and today.
Despite its dynamic-sounding name, the acronym stands for the less stirring Cabinet Office Briefing Room A".
The Home Office was not disclosing details of the latest meetings or whether they took place in 10 Downing Street.
If Whitehall is considered in danger, Cobra can be re-located to the Citadel - the secure underground complex below government buildings in the area.
Terrorism has been behind most of the recent needs for Cobra to meet.
Tony Blair was rushed back to London from the G8 summit in Gleneagles by helicopter on July 7 last year to chair a session in the aftermath of the bombings in the capital.
It was reconvened after the failed attacks two weeks' later.
Its most recent role before today came in April, when it discussed the discovery that a dead swan found in Scotland had the deadly H5N1 strain of bird flu.
The committee would initially need to consider whether to invoke the powers contained in part two of the Civil Contingencies Act, which allows considerable powers for the executive in times of a serious emergency.
They were designed to cope with a far larger strike, particularly one involving chemical or radiological material, such as a nuclear "dirty bomb".
Under those powers, sittings of Parliament could be suspended if necessary and a bank holiday declared to shut down businesses.
By executive decree, property could be destroyed or requisitioned, assemblies banned, freedom of movement limited, the Armed Forces mobilised and special courts set up to deal with suspects if it was felt another atrocity was planned.
Although he is in charge of the country while Mr Blair is on holiday, Deputy PM John Prescott did not attend today's meetings, instead being briefed afterwards.