“(7) If a person who, apart from this subsection, would be liable to a surcharge under subsection (4) above satisfies the Commissioners or, on appeal, a tribunal that, in the case of a default which is material to the surcharge – (a) the return or, as the case may be, the VAT shown on the return was despatched at such a time and in such a manner that it was reasonable to expect that it would be received by the Commissioners within the appropriate time limit, or (b) there is a reasonable excuse for the return or the VAT not having been so despatched, he shall not be liable to the surcharge and for the purposes of the preceding provisions of this section he shall be treated as not having been in default in respect of the prescribed accounting period in question (and, accordingly, any surcharge liability notice the service of which depended upon that default shall be deemed not to have been served). (8) For the purposes of subsection (7) above, a default is material to a surcharge if – (a) it is the default which, by virtue of subsection (4) above, gives rise to the surcharge; or (b) it is a default which was taken into account in the service of the surcharge liability notice upon which the surcharge depends and the person concerned has not previously been liable to a surcharge in respect of a prescribed accounting period ending within the surcharge period specified in or extended by that notice.”