“ an applicant ... that has failed to comply with such an obligation or request as is referred to in subparagraph (1) is to be treated as satisfying the condition and that subparagraph as regards that obligation or request if the Board of the Inland Revenue of the opinion that -- (a) the applicant ... had a reasonable excuse for the failure to comply, and (b) if the excuse ceased, he ... complied with the obligation or request without unreasonable delay after the excuse had ceased.”
“(1) payment is made not later than 28 days after the due date, and (2) the applicant has not otherwise failed to comply with this obligation within the previous 12 months.”
“(2)… for the purposes of this Act, a person shall be deemed not to have failed to do anything required to be done within a limited time if he did it within such further time, if any, as the Board or the Commissioners or officer concerned may have allowed; and where a person had a reasonable excuse for not doing anything required to be done he shall be deemed not to have failed to do it unless the excuse ceased, and after the excuse so ceased, he shall be deemed not to have failed to do it if he did it without unreasonable delay after the excuse had ceased.”
“ the amount of the payments on account required to be made shall be, and shall be deemed always to have been, equal to 50% of the stated amount.”