The head of the security service MI5 said today that Britons face a "serious and sustained threat" of terror attacks at home and abroad.

Eliza Manningham-Buller told business leaders at the annual CBI conference that despite the arrest and killing of many senior al-Qaeda leaders, the organisation behind September 11 can still mount attacks.

And the danger had continued to grow because Osama bin Laden’s group has "inspired" other fanatics.

"There is a serious and sustained threat of terrorist attacks against UK interests at home and abroad, including against the business community," said the MI5 chief.

"There might be major attacks like Madrid earlier this year. They might be on a smaller scale. The terrorists are inventive, adaptable and patient. Their planning includes a wide range of methods to attack us.

"Many senior al-Qaeda figures have been killed or arrested since 9/11 but, although the organisation has been damaged, it retains the capability to mount terrorist attacks on Western interests.

"Moreover, the international terrorist threat that manifests itself in other forms which are as challenging. Al-Qaeda has become shorthand for other terrorist groups or networks that, inspired by Al-Qaeda’s successes, and in imitation of it, are now planning attacks against Western interests."

People would rightly question the level of threat and particularly the possible scale of any attack, said Ms Manningham-Buller.

"But I would urge you to consider the events of 9/11, in Bali, in Istanbul, in Madrid. Be under no illusion. The threat is real and here and affects us."

Counter-terrorism had helped to prevent attacks in Britain since the New York and Pentagon strikes, she continued. The Government had also made it more difficult for terrorists to operate in the UK.

"Responding to the threat has not been easy, and difficult judgments have to be made," she said.

"Balancing liberty against security is perhaps the most difficult of them. But stopping an atrocity is only one aspect of the challenges we face.

"Across the UK, private companies are working with the service and the police to increase resilience and strengthen the capacity of the private sector to stay in business in the face of threats or actual attacks."

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