CG77520 | Found objects and treasure: ownership
From HM Revenue & Customs · Capital Gains Manual
A claim to the ownership of a found object might be made by
the original owner of the object or his or her heirs
the Crown
the finder of the object
the owner of the land where the object was found.
This can be a complex area of law. You will sometimes find that the persons who might have title to the object are unable to determine ownership and leave the question unresolved.
If the question of ownership has been resolved between the parties you should usually accept their view and deal with the Capital Gains Tax consequences in accordance with the guidance at CG77560+.
Ownership can be a contentious issue in these cases and you should not take sides. You should ensure that each of the interested parties is dealt with consistently.
If ownership has not been resolved, or is unclear from the information with which you have been provided, the summary below for simple cases will help you to understand the position of each party: