under Chapter II of part XIV of the 1996 Act, the amount of a week’s pay of an employee falls to be calculated by reference to the average rate of remuneration, or the average amount of remuneration, payable to the employee in respect of a period of twelve weeks ending on a particular date (referred to as “the calculation date”);

during a week in that period, the employee was absent from work on ordinary or additional maternity leave or parental leave, and

remuneration is payable to the employee in respect of that week under her contract of employment, but the amount payable is less than the amount that would be payable if she were working,