By Angus Roxburgh BBC News Online, Brussels

If all was well in the European Union, it would not be Tony Blair who was heading for crisis talks on Iraq at President Bush's Camp David retreat this Friday.

It has been much harder for European nations to sink their differences on foreign policy than on the economy, trade or the environment

It would be Javier Solana, the EU's "high representative" for foreign policy, or Chris Patten, the external relations commissioner - or some other "Mr CFSP", as the job used to be known, referring to the EU's aspired-to "common foreign and security policy".

The job description has remained as unwieldy and unconvincing as its title, for efforts to create a common foreign policy have stumbled ever since the EU agreed to have one, in Maastricht in 1992.

Partly to blame is the EU's system of rotating six-month presidencies. Every half-year a new country takes over, with its own priorities and its own view of the world.

Confusion on Africa

The creation of a coherent foreign policy is just one of the reasons why most of the large powers in Europe are now in favour of a longer-term EU "president" of some description, who would have greater visibility and lend the union's external relations a degree of continuity.

The EU risks an embarrassing display of disunity over Zimbabwe

But the main reason for the disarray is that it has simply been much harder for major European nations to sink their differences when it comes to projecting their power abroad, than it is to agree common policies on the economy or trade or the environment.

This week, an attempt by the EU's foreign ministers to renew sanctions against Zimbabwe collapsed because France wanted an exemption from the travel ban to enable President Robert Mugabe to attend a Franco-African summit in Paris.

The EU's whole relationship with Africa was thrown into confusion, with an EU-Africa summit to be hosted by Portugal in April under threat. If France was allowed to receive Mugabe, the Portuguese wanted the same right.

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Where key nations stand on Iraq

But the leaders of the UK, Germany, Denmark, Sweden, the Netherlands and Spain are all likely to boycott a summit attended by Mugabe, which would transform the event into an embarrassing display of European disunity.

Macedonia mission

The foreign ministers did agree an anodyne text on Iraq. They called on Saddam Hussein to co-operate with the UN weapons inspectors, but glossed over their deep differences regarding when or whether to go to war against him.

Tony Blair is in a position of enormous influence

The trouble with a common European foreign policy is that it represents (or would represent, if it existed) a major step towards pan-European government, since it would endow the EU with yet more attributes of statehood, so despised by euro-sceptics.

Logically, if there really was a single foreign policy, there would be no need for national embassies abroad, only EU ones.

There are some successes. The EU will shortly, after much delay, take on its first joint military mission, in the former Yugoslav republic of Macedonia.

But otherwise, the military side of CFSP has been mired in wrangling over relations with Nato, finances and political leadership.

Blair role

In the absence of a serious defence capability, Nato remains the chief military instrument for most EU countries. But the rifts within Nato reflect those within the EU.

George W Bush knows exactly who to ring in a crisis - it is Tony Blair.

This week, several of America's allies refused to go along with a proposal that Nato should begin planning for the event of war against Iraq. France and Germany thought that would send the wrong signals while diplomatic efforts to resolve the crisis were not yet exhausted.

The old cliche used to justify the establishment of a common EU foreign policy is that an American president needs to know who in Europe to ring in a crisis.

Well, George W Bush knows exactly who to ring. It is Tony Blair.

That puts the British prime minister in a position of enormous influence. He may not be entirely in step with other Europeans, but he is not totally in line with the White House either, and he is the only European capable of influencing American policy at this time.

Mr Blair has been preparing for his Camp David "council of war" with Mr Bush by consulting all his European colleagues, and there is no-one better placed to convey their views to the Americans.

He is, effectively, for the time being, Europe's Mr CFSP.