The teachers had argued that the 1870 Apportionment Act limited deductions from their pay in respect of one day’s strike action in November 2011 to 1/365 of their annual salaries. Their employer, King Edward VI School in Stourbridge, had deducted 1/260 as “the value of the service which the teachers had failed to provide on that day”, discounting weekends and holidays and basing the calculation on the premise that their working days were Monday to Friday.

In a unanimous judgment, the Supreme Court ruled that the teachers’ salaries were “entire indivisible payments” which accrued day by day over the course of the year at an equal rate.The Supreme Court’s judgment overturned that of the Court of Appeal, which had assumed in its approach that the teachers only worked during their “directed” teaching hours. The teachers were also required to perform other “undirected” work, including marking work, writing reports and preparing lessons. This often happened at weekends.

The 1870 Apportionment Act provides that periodic payments, rents, annuities or dividends accrue on a daily basis. The section related to “annuities”, which includes “salaries and pensions”, states payments that can be apportioned should be deemed to have accrued “by equal daily increment”. However, parties can contract out of the rule in certain circumstances by “express stipulation”.

Chris Keates of the teachers’ trade union, NASUWT, described the judgment as a “landmark victory for teachers’ rights across the UK”.