Britain is taking back control of its nuclear weapons.
Since 1999 the warheads for the submarine-based deterrent have been maintained by a U.S.-led consortium.
Defence giant Lockheed Martin owns just over half of that.
British firm Serco and Jacob’s Engineering of the U.S. share the rest.
Now London says it is ending the arrangement earlier than expected.
It says that will have benefits including better value for money for taxpayers.
Serco says it was told about the termination late Friday (October 30).
On Monday (November 2) its shares tumbled around 13%.
Based in Aldermaston and Burghfield in southern England, the Atomic Weapons Establishment has long been a focus for anti-nuclear protests.
It develops and maintains the warheads that are fitted to the UK’s Trident missiles.
Sky News, which first reported the story, said it wasn’t clear if the companies would be compensated for early termination of the 25-year contract.