The Sri Lankan Government has apparently made a fresh request that artefacts in British Museums be returned. This request has been made before but Britain has not responded.
Given the fact that Sri Lanka's politicos were almost certainly complicit in the robbery of the Colombo Museum, I think there is a very good case for leaving them where they are. Why should they be returned, if they are only to be stolen and either sold or used to decorate the houses of the politikka's who are now competing with one another to build palatial houses in Colombo 7?
Better that they be kept safe and secure in museums overseas, where they can be studied and enjoyed by humanity at large.