The Prime Minister, sitting alongside President Jacques Chirac and the French Prime Minister, Lionel Jospin after a successful and good-natured - almost high-spirited - Anglo-French summit, called the agreement "historic". The word is justified for two reasons.
This was the first time France and Britain had joined forces to push for the creation of an important new EU policy. The St Malo Declaration lays the foundations for Europeans to intervene in regional crises - either as trouble-shooters or peace-keepers - when the United States refuses to get involved. If accepted by other European countries and the US, such a policy would give the EU an effective, common foreign policy for the first time; one capable of backing words with actions.
Both Tony Blair and the French leaders insisted that the intention was not to replace or weaken Nato. Responsibility for the overall defence of Europe would remain with the Western alliance.
But EU summits and councils of foreign and defence ministers would be able to take decisions - from which dissenting governments could stand aside - to deploy forces to deal with regional crises (on the pattern of Kosovo or Albania). The Anglo-French statement, considerably stronger than seemed possible earlier in the week, said: "The Union must have the capacity for autonomous action, backed up by credible military forces, the means to decide to use them, and a readiness to do so, in order to respond to international crises."
During his tete-a-tete with Mr Chirac on Thursday night, Mr Blair said it was "bizarre" that a regional power such as the EU should have a single market, a single currency and a single foreign policy but no defence policy. The Prime Minister had signalled in October that he was prepared to abandon the opposition of successive British governments to any EU encroachment into defence and military matters.
"Britain is forging a new relationship in Europe," Mr Blair said yesterday. "That is good for Britain. I hope it is good for Europe too. I have no doubt at all that that is where the future interests of my country lie."
EU troops sent to intervene in regional crises would be taken from those committed to Nato; or from national forces outside Nato (that is, the French) or from the minimal logistics capacity of the existing, rather ineffectual, European defence arm, the Western European Union (WEU). The statement also commits France and Britain to push for the creation of new, specifically European capacities for intelligence-gathering, analysis, strategic planning and transport. The bulk of such capabilities in Nato at present is in American hands.
The question of who would manage this military side - as opposed to the decision-making, political side - of the EU defence policy was left deliberately unclear. The Secretary of State for Defence, George Robertson, said afterwards that three options remained open. First, the WEU would be beefed up with the new logistic resources but remain as a separate institution; second, a stronger WEU should be absorbed into the structures of the EU; third, the WEU should disappear and be carved up between the EU and Nato. The French prefer the "all EU" option; Britain says that its mind remains open.
What remains to be seen is how other EU governments - and the US - will respond. The Germans, though perhaps rather wary of seeing Britain and France usurp the normal Franco-German role of European trail-blazer, have said they are broadly in agreement with the embryo defence policy. The neutral EU countries, Ireland, Sweden, Finland and Austria, will have problems but could stand aside if they wish.
The US has given Britain a green light but will be wary of any signs that an EU defence policy is emerging as a rival to Nato, either politically or as a recipient of military spending. The next big test of the Franco- British ideas will be the Nato summit in April, when Britain hopes the Europeans will have a more fully developed plan to put before the Americans.