EU members take turns to provide most of the troops for the EU defence force and Britain was meant to take responsibility during the final months of the Brexit transition period in 2019.
Britain’s Lieutenant General George Norton’s letter said the decision to withdraw is due to uncertainty brought from the Brexit transition.
But Britain could still be part of the program depending on the political agreement that comes after we leave the EU.
Mr Norton added the UK’s offer to head the EU defence force was always “provisional”.
He wrote to the Chairman of the EU military committee General Mikhail Kostarakos: “Military activities, however, require clarity of purpose and planning; not least of which involved the time that is necessary to force generate credible capabilities.
“The UK believes that, for the practical purpose of the time needed for the EU and member states to identify and assign a stand-by battlegroup for the second half of 2019, a decision should know be delayed.
“Consequently we formally withdraw our provisional offer of a battlegroup for the period 2019-2020.
“Our prime minister’s unconditional commitment to European security of course stands, but the offer of a battlegroup in the period immediately following our exit strikes as an unnecessary complication.”
The letter, obtained by Politico, came despite insistance that Britain will cooperate on security issues after Brexit.
Last month Mrs May said at the Munich Security Conference: “The UK is just as committed to Europe’s security in the future as it has been in the past.
“It’s in all of our interest to underpin this cooperation.”
UK officials have said that Britain’s continued involvement after Brexit would largely depend on whether the UK can negotiate to have more involvement and control of military missions.
Allies in the EU united against Russia after the Salisbury poisoning attack, with a joint statement from France, Germany and the United States attacking “irresponsible” Russia for the “first offensive use” of a military-grade nerve agent.