Gains: disposal of found objects: chattels
Objects of the type dealt with in these instructions, found lying on the land or buried in the soil, remain chattels for the purpose of Capital Gains Tax. Even if ownership of these objects arises from ownership of the land in which they are found, see CG77520 the objects are still chattels. Whether they were originally hidden or lost there will not have been any intention that they should be permanently affixed to the land. So they are not fixtures.
Because such an object is a chattel the chattels exemption, explained at CG76550+ applies.
If you need a valuation of a found object to compute the gains arising in accordance with this chapter, see CG77000+.