Found objects: ownership: objects not treasure or treasure trove: ownership of object not resolved
CG77540 explains that depending on the circumstances the landowner and the finder of an object may each have a claim to it. If they have not been able to resolve their claims you should follow the advice at CG77520.
Sometimes each of them will agree to abandon their claim to ownership of the object in exchange for a share of the disposal proceeds. When this happens their share will be a capital sum derived from an asset, being their rights under the agreement. The taxation consequences are explained at CG77610.