In a statement released by the UK government on 24 January 2025, the Department for Energy Security and Net Zero announced that it "will work with the Nuclear Decommissioning Authority (NDA) to immobilise the UK-owned civil separated plutonium inventory at Sellafield."

This announcement marked a shift in the UK approach to plutonium disposition. In 2011, the government made a preliminary decision to use the plutonium in MOX fuel, but also stated that it is open to other options. Immobilization was under consideration in 2015 (see the IPFM post), but no decision was made at the time.

As of the end of 2023, the United Kingdom had 140.9 tonnes of separated plutonium in its custody. Of this material, 24.1 tonnes belonged to other states, most of it - 21.735 tonnes - to Japan. The United Kingdom shut down the THORP plant that was reprocessing oxide-based fuel in 2018 and the Magnox plant in 2022.