28(1)If the Inland Revenue discover as regards a chargeable transaction that—
(a)an amount of tax that ought to have been assessed has not been assessed, or
(b)an assessment to tax is or has become insufficient, or
(c)relief has been given that is or has become excessive,
they may make an assessment (a “discovery assessment”) in the amount or further amount that ought in their opinion to be charged in order to make good to the Crown the loss of tax.
(2)The power to make a discovery assessment in respect of a transaction for which the purchaser has delivered a return is subject to the restrictions specified in paragraph 30.