UK's stern foreign policy test

Mr Blair: Attack was "on the democratic world"

Britain's pledge to stand "shoulder to shoulder" with America in the aftermath of the devastating terrorist assault could have far-reaching implications for foreign relations, a leading expert has warned.

Tuesday's attacks are likely to have the biggest impact of any single event on international relations since Pearl Harbor, according to Professor Victor Bulmer-Thomas, director of London's Royal Institute of International Affairs.

You have to go back to Pearl Harbor for something like this - and there at least the enemy was visible and identified

Professor Victor Bulmer-Thomas

He predicts major implications for a host of high-profile issues, from President Bush's planned missile defence project to the future of European defence co-operation.

Offering firm support across the Atlantic on Tuesday evening, Mr Blair said the UK would "stand shoulder to shoulder with our American friends in this hour of tragedy and we like them will not rest until this evil is driven from our world".

Casting mass terrorism as the new evil facing the world, he said there was now a battle "between the free and democratic world and terrorism".

Forcible retaliation

The consequences of offering such strong support, which could include military action, cannot be accurately gauged yet, Professor Bulmer-Thomas told BBC News Online.

"It very much depends on how the United States retaliates but I think we can assume they will retaliate and very forcibly so.

"The danger is they do it far too early, before the facts are in.

Mr Blair says the attacks on US buildings were an attack on the world

"I hope that is not on the cards but if it is, and there is no doubt that the American people will demand action quickly and forcibly, that will put pressure on US allies to line up behind them.

"I think that we know about Tony Blair, and indeed previous British governments, when the US is in a crisis like this they don't ask questions, they give unconditional support."

Even as America reels from the shock of the attacks, the pledge of support from Mr Blair would be much appreciated, says Professor Bulmer-Thomas.

Military ally

"Not so much by the American people, who have other things to worry about, but the US administration do need to know they have at least one ally - it will be very important in military and intelligence terms if nothing else."

However, the Institute of International Affairs director thought Mr Blair's talk of a battle between "the free and democratic world and terrorism" less helpful.

"That would worry me. In this situation one needs the support of all responsible governments."

Some other European Union nations will be extremely nervous about the scale of any retaliatory action

Professor Victor Bulmer-Thomas

China - one of the United States greatest rivals - will have just as much interest in catching the perpetrators, he believes.

Russia, with its own scarring experience of terrorism triggered by conflict in Chechnya, will be sympathetic and probably offer intelligence assistance to the Americans.

But Professor Bulmer-Thomas also predicted problems for Britain closer to home with unconditional backing for US military retaliation.

With some European neighbours likely to be "extremely nervous", effects will be felt on, for example, the proposed European rapid reaction force.

Missile defence

"If two major European countries do not see eye-to-eye in response to US actions, it is hard to see how they could see eye-to-eye on creating a common European defence and security capability."

Tensions could also be raised with Commonwealth countries and other nations friendly to Britain across the globe.

The debate over President Bush's missile defence programme, controversial in Britain in case it involves UK-based installations, will also be affected.

Professor Bulmer-Thomas said: "Those sceptical about missile defence will say: 'I told you so, a determined enemy can through any military capability, no matter how sophisticated.

"But their opponents will say when dealing with such irrational and irresponsible enemies, missile defence can ward off some of these threats."