(1)This section applies if—
(a)an assessment to income tax is made as respects relevant income (with or without other income), and
(b)the assessment is made after the end of the period of 12 months following the tax year for which it is made.
(2)In so far as it relates to relevant income, the assessment is to be made in accordance with the practice generally prevailing at the end of that period.
(3)“Relevant income” means income which—
(a)has been taken into account in the making of deductions or repayments of tax under PAYE regulations, and
(b)was received not less than 12 months before the beginning of the tax year in which the assessment is made.