143Deduction for periods when car unavailableU.K.
(1)A deduction is to be made from the amount carried forward from step 6 of section 121(1) if the car has been unavailable on any day during the tax year in question.
(2)For the purposes of this section a car is unavailable on any day if the day—
(a)falls before the first day on which the car is available to the employee,
(b)falls after the last day on which the car is available to the employee, or
(c)falls within a period of 30 days or more throughout which the car is not available to the employee.
(3)The amount of the deduction is given by the formula—
where—
U is the number of days in the year on which the car is unavailable,
Y is the number of days in that year, and
A is the amount carried forward from step 6.
(4)This section is subject to section 145 (modification where car temporarily replaced).