Defence Secretary Geoff Hoon today announced an urgent review of the Armed Forces in the light of the US terror attacks.

Mr Hoon told the Labour Party conference that they may need to "re-balance" Britain's existing military capabilities in order to deal with the new threat of global terrorism.

He said: "We must have the right concepts, the right levels of forces and the right capabilities to meet the additional challenges we face from international terrorism conducted on this scale."

Ministry of Defence sources said the review would be "evolutionary not revolutionary".

Mr Hoon said it would increase the post-Cold War emphasis on "rapidly deployable, flexible forces" able to deal with a crisis anywhere in the world.

He said: "No one anticipated a threat on scale of the threat we are now having to deal with. No one either anticipated the kind of fanaticism we saw on display in those appalling scenes on September 11. We are dealing with a very different world."

He said the review would also have to look at the implications for Britain home defences.

The review is likely to emphasise the need for improved intelligence gathering capabilities.

However defence experts dismissed suggestions that it would mean a significant expansion of the SAS.

The special forces' stringent recruitment requirements mean that there was only very limited scope for increasing their numbers without diluting their quality.