The Bona Vacantia list is published on the gov.uk website:-
https://www.gov.uk/government/statistical-data-sets/unclaimed-estates-list
These are cases where people have died and no-one has come forward to administer the estate (usually because there is no Will and no relatives). Generally, they are referred to the Treasury Solicitor by local councils and asset holders. They can appear years after death - the cut off point is 30 years, I think.
I successfully claimed a BV estate for a friend about 15 years after his father's death (they had been estranged).