On a claim being made in that behalf by the appropriate person there shall be determined for the purposes of this Chapter the amount (if any) by which—
Subject to the following provisions of this Chapter, in determining the tax chargeable on the death in question, the value of the investments to which the claim relates shall be treated as reduced by an amount equal to the loss on sale.
A claim under this Chapter must be made not more than 4 years after the end of the period mentioned in subsection (1)(a).
A claim made by the appropriate person under this Chapter shall specify the capacity in which he makes the claim, and the reference in subsection (1) above to qualifying investments which are sold by him is a reference to investments which, immediately before their sale, were held by him in the capacity in which he makes the claim.