15This paragraph applies where, at the time the buyer ceases to be a member of the same group as the seller (“the relevant time”), it or a relevant associated company holds a chargeable interest—
(a)that was acquired by the buyer under the relevant transaction, or
(b)that is derived from a chargeable interest so acquired,
and that has not subsequently been acquired at market value under a chargeable transaction for which relief under this schedule was available but not claimed.