Gordon Brown has had a baptism of fire in his first 48 hours as Prime Minister, with the death in Iraq of soldiers from his own home area of Fife and now an apparent terrorist bomb attempt on Central London.

The new leader has had to come to grips speedily with the violent realities of opposition to Britain and its policies abroad.

On his way to his second Cabinet meeting, Mr Brown stressed that the public must be vigilant.

"The first duty of government is the security of the people, and as the police and security services have said on so many occasions, we face a serious and continous threat to our country," said Mr Brown.

"The incident does recall to me that we must be vigilant at all times and the public must be alert for any potential incident. I will stress to the Cabinet that this vigilance must be maintained over the next few days."

Mr Brown said that Jacqui Smith, the new Home Secretary, would chair a meeting of Cobra, Britain’s emergency contingencies committee, and then brief the Cabinet.

Ms Smith issued a brief statement, saying: “Obviously the police are investigating and I think we should all allow them to get on with that without undue speculation."

She too has had a rude introduction to her new job, woken in the small hours by a call from the security services to brief her on the unfolding incident. Any hopes of spending her first full day in the post getting to grips with her inbox and receiving briefings from her civil servants will have flown out of the window.

She will be at the centre of Whitehall's efforts to find out as much as possible about the bomb plot, and to decide how to react to what may well be a disturbing shift in direction by al-Qaeda linked terrorists on British soil.

Her reaction will be guided by Cobra, which comprises ministers and expert senior officials from across the Government.

However, Mr Brown has also made clear that when it comes to protecting the country he will “take the lead”.

"We assume that the motive behind the attack was to test the new Government, and it must now show that it has machinery in place to react to what has happened," said Philip Webster, Times Political Editor.

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