The violent response that the Americans demanded to the events of September 11 has so far been measured, focused and careful. The coalition's initial aims will include eliminating the Taleban's ability, albeit limited, to fly any form of combat plane.

It will also be trying to remove the regime's capability to conduct anti-aircraft operations - giving the Americans greater freedom to go after other targets and enabling humanitarian aid to get through.

You can expect a significant reaction throughout the wider Islamic world - demonstrations at US and British consulates - mostly not favourable to the coalition cause.

There is also the possibility of a signature retaliatory terrorist event.

Coalition ground forces will be committed to the war in Afghanistan, but probably not in large numbers. This low-key special forces approach is likely to pose significant problems for coalition governments.

There will be no quick return in the shape of burning vehicles for the public to see. Maintaining the home front will be a problem, especially for the US, where public opinion is volatile and a vital political ingredient.

Politicians and the public have an unrealistic expectation of low casualties. There will be casualties, particularly when ground forces are involved. The territory is hostile, the Taleban are hardened fighters and history shows that when a country is invaded the populace fights back no matter how despotic their ruler.

I am optimistic the Taleban can be toppled within six weeks, before 'General Winter' takes the field - and operations in winter are unusual in Afghanistan - but that will not be the end of it.

It is likely there will be a resistance movement and the Americans will not rest until they have Osama bin Laden or his body. Finding bin Laden will take some doing - he will have his game plan ready and has had years to work on it.

I think the war against terrorism can be won, but it could go on forever. When one terrorist falls, another rises in his place and they are not just in Afghanistan but all over the world. It is a mistake to think terrorists are just bearded weirdos. They are rational. Good intelligence will be vital to combat them.

When I started fighting the IRA in 1970, we thought it would be over in two or three years, and 30 years later it is still going.

I worry whether the Americans have the guts to keep fighting for as long as it is going to take - because Afghanistan is only phase one in this war. Hopefully they do, but the ghosts of the Vietnam War linger on.

There is a risk the coalition could inherit the humanitarian situation created by the Taleban as pictures of starving children and dead or dying women take hold - and the forces could be blamed instead of thanked for their efforts.

Another concern is that the coalition could get bogged down in fighting this unconventional war in a conventional way.

An unconventional approach could be, for example, to have captured all the mullahs when they met to consider whether to hand bin Laden over.

Grave choices face both the leaders and the public. Are we prepared to use methods less palatable than those we are used to? Victory against terrorism may require acts which do not lie easily with the moral background of those from democratic nations.