(1)If—
(a)an individual’s spouse or civil partner is entitled to a tax reduction under section 45 or 46 for a tax year,
(b)the spouse or civil partner’s MCA tax reductions are greater than the spouse or civil partner’s comparable tax liability, and
(c)the conditions set out in subsection (4) are met,
the individual is entitled to a tax reduction for that tax year equal to the unused part of the spouse or civil partner’s MCA tax reductions.
(2)The spouse or civil partner’s MCA tax reductions are the sum of—
(a)the tax reduction to which the spouse or civil partner is entitled under section 45 or 46, and
(b)any tax reduction under section 49 to which the spouse or civil partner is entitled for the tax year.
(3)The unused part of the spouse or civil partner’s MCA tax reductions is equal to—
(a)the spouse or civil partner’s MCA tax reductions, less
(b)the spouse or civil partner’s comparable tax liability.
(4)The conditions are that—
(a)the spouse or civil partner gives notice to an officer of Revenue and Customs that subsection (1) is to apply for the tax year,
(b)the individual makes a claim, and
(c)the individual meets the requirements of section 56 (residence etc).
(5)The tax reduction to which the individual is entitled under subsection (1) is in addition to any tax reduction to which the individual is entitled under section 47 or 48.
(6)The meaning of “comparable tax liability” is given in section 53.