This is a very tough world with an enemy that's determined to hit us

Mr Bush said "the realities of sitting in the Oval Office are different from the realities of the campaign, of being on the campaign trail".

"This is a very tough world with an enemy that's determined to hit us. And a president who listens to the intelligence being gathered will realise that the main job for the president here in this part of the 21st century is to defeat the enemy by staying on the offence and, therefore, securing America," he said.

He predicted a long ideological struggle facing successive presidents.

"Presidents are going to have to keep the pressure on al-Qaeda by using good intel and finding him and pressuring him. At the same time, presidents are going to have to promote ... an alternative ideology to that espoused by these extremists and radicals, and that happens to be one based on liberty."

During a wide-ranging interview yesterday in the conference room aboard Air Force One, Mr Bush reflected on his time in office thus far, with less than 20 months left.