The UK will lose command of the EU naval task force – set up to combat piracy off the coast of Somalia – as it exits the European Union.
The headquarters – currently in Northwood, north London – will move to Rota in Spain, with some operations heading to Brest, in France.
The European Council made the move “following the decision by the UK to withdraw from the EU”.
The council has extended its mission until 2020, but will continue from its two new hubs from the spring of next year, led by Spanish Vice Admiral Anotnio Martorell Lacave.
Its current operational commander, Major General Charlie Stickland, said: “The transition is being planned with the utmost consideration to ensure it is smooth and seamless with continued cooperation and collaboration with all stakeholders throughout the region.”
BBC defence correspondent Jonathan Beale said the move was “not a surprise to the UK”, which is due to leave the EU on 29 March 2019, but it is “still a blow”.
He said the statement from Navfor left “no doubt” that the move was because of Brexit,
He added: “The government has signalled it is still willing to contribute to future EU defence and security operations.