Found objects and treasure: ownership: introduction
The following guidance deals with the application of Capital Gains Tax to sums received as a result of the discovery of objects on a person’s land. Typically the cases you will see will involve historical or archaeological artefacts; hoards of gold coins, medieval jewellery, and the like. Commonly the objects will have been found by the use of metal detectors, although this guidance is not limited to such cases.
The guidance at CG77520+ provides basic advice on the ownership of such objects including an overview of the law of treasure and of treasure trove.
The guidance at CG77560+ explains how any gains are computed once the question of ownership has been resolved.