The senior Cabinet minister urged his European counterparts only to back military moves that bolster the North Atlantic Treaty Organisation.
He issued the warning after European Commission boss Jean-Claude Juncker argued after Donald Trump’s election as US president that the EU could not rely on America in the long term for its security and so needed a “new start” in defence up to creating a “European army”.
But Sir Michael said: “Britain will only support proposals to strengthen European security that complement Nato, not duplicate it.
“That means doing more to improve Nato-EU co-operation on cyber, hybrid threats, and maritime security.
“But loose talk of an EU Army risks undermining Nato and we will go on opposing this - backed up by many other member states.”
Britain commits two per cent of GDP to military spending and Sir Michael, speaking before a meeting of foreign and defence ministers in Brussels, urged other EU nations to do the same.
His remarks were echoed by Foreign Secretary Boris Johnson who warned against undermining
the “fundamental security architecture that has looked after us for 70 years”.
He also said the election of Mr Trump represented a “moment of opportunity” for Britain and for Europe.
“There is a lot to be positive about and it is very important not to prejudge the president-elect or his administration,” he stressed.
“It’s up to us and everybody to…take things forward in a positive way.
“Donald Trump is a dealmaker and I think that could be a good thing for Britain, but it could also be a good thing for Europe.”
