Britain will pull out of a major foreign policy arrangement as soon as possible after Brexit, Theresa May has announced.
The Prime Minister said the UK would not wait until the end of any implementation period to take back full control over areas like diplomacy, peacekeeping, defence and aid.
Common policy on foreign and security areas grew out of the Maastricht Treaty so the move is likely to please Brexiteers.
But Mrs May stressed that Britain will continue to work closely with the EU on security and said the UK's commitment to protecting Europe from threats is "unconditional".
Mrs May said: "There is no reason why we should not agree distinct arrangements for our foreign and defence policy co-operation in the time-limited implementation period as the Commission has proposed."
She added: "We shouldn't wait where we don't need to."
The system meant that Britain was forced to take part in a summit in 2003 in Lisbon despite protesting over the attendance of Zimbabwean dictator Robert Mugagbe. Gordon Brown boycotted the event but the government was obliged to send a representative.
But in practice the UK is still expected to maintain very close cooperation.
No 10 sources insisted the move was about regaining sovereignty.
Mrs May said: "In particular, we will want to continue to work closely together on sanctions. We will look to carry over all EU sanctions at the time of our departure.
"Second, it is clearly in our shared interests to be able to continue to co-ordinate and deliver operationally on the ground.
"Of course, we will continue to work with and alongside each other. But where we can both be most effective - by the UK deploying its significant capabilities and resources with and indeed through EU mechanisms - we should both be open to that.
"On defence, if the UK and EU's interests can best be furthered by the UK continuing to contribute to an EU operation or mission as we do now, then we should both be open to that.
"And similarly, while the UK will decide how we spend the entirety of our foreign aid in the future, if a UK contribution to EU development programmes and instruments can best deliver our mutual interests, we should both be open to that.
"But if we are to choose to work together in these ways, the UK must be able to play an appropriate role in shaping our collective actions in these areas."
Mrs May also called for an "open and inclusive approach" on defence capability projects.