The United Kingdom published information about its holdings of civilian plutonium and HEU as of December 31, 2012. These numbers will be later submitted to IAEA as an INFCIRC/549/Add.8/16. [UPDATE 07/19/2013: The document was published on the IAEA site on 19 July 2013.]
According to the published data, as of the end of 2012 the U.K. had 116.1 tonnes of separated unirradiated plutonium at the reprocessing facilities, 1.2 tonnes in unirradiated MOX fuel and 1.9 tonnes in the MOX fuel manufacturing process. Additional 1.0 tonne of unirradiated plutonium is "held elsewhere." These numbers apparently include the 4.4 tonnes of plutonium that the United Kingdom declared as excess to its national security needs.
Of this total of 120.2 tonnes, 23.8 tonnes belonged to foreign countries. In addition, the U.K. had 0.9 tonnes of its plutonium outside of country. No material was in transit.
The total amount of separated civilian Pu in the UK is 120.2 tonnes (118.2 tonnes in 2011), the total amount of UK owned plutonium is 97.3 tonnes (91.2 in 2011). The increase of the UK owned Pu reflects the result of a series of title swaps, performed in July 2012, in which "about 4 tonnes" of plutonium that belonged to Germany were transferred to the UK custody, while equivalent amount of Pu was made available to Germany in France. The numbers, however, does not take into account the April 2013 title swap.
In addition, the United Kingdom declared 7 tonnes of plutonium in spent fuel held at reactor sites (8 tonnes were reported in this category in 2011), 24 tonnes - in spent fuel at reprocessing plants awaiting reprocessing, and less than 500 kg - in spent fuel held elsewhere.
The report also contains information about civilian HEU holdings - the United Kingdom had 1396 kg of the material, down from 1400 in 2011. Of this HEU, 343 kg is at fabrication plants (346 in 2011), 912 kg - at laboratories and research facilities, 10 kg - irradiated HEU at civilian reactor cites, and 131 kg - irradiated HEU at other sites.