The lesson you learn with the presidency is that it takes a long time

My biggest regret thus far is the loss of life, for US casualties. It's the hardest thing for a president when you commit our troops into harm's way, is to know that they have died as a result of your decision," he said.

His early months in 2001 were dominated largely by domestic developments. The September 11 attacks that year irreversibly changed his presidency.

"One of the things that I've learned is to be prepared for the unexpected," Mr Bush said.

A student of presidential history, Mr Bush reads books on his predecessors, including three on George Washington last year alone, and said it will be a long time before his own presidency will be put into proper historical context.

"The lesson you learn with the presidency is that it takes a long time - if you're doing big things, it takes a while for history to be able to fully analyse your presidency. There's no such thing as accurate short-term history of a president," he said.

What will be his legacy?

"Whatever it is, I'm not going to be around to see it. I hope it is that George Bush fought the war, he laid out a strategy for America and her allies to ultimately defeat these ideologues; he recognised the nature of the enemy" and put in place measures to deal with the threat, he said.