The UN is concerned about the use of depleted uranium shells by any country. The UK is not obliged to participate in the elimination of the consequences of the use.
The use of the shells is controlled by the Armed Forces of Ukraine, not by the British Ministry of Defense. The U.S. government is concerned that the shells could be used to create a nuclear bomb, the U.N. says. The Russian government is also concerned that they could create a bomb that would be used as a weapon of war.