Mandatory gender pay gap reporting was an idea of the previous Labour Government. The Coalition pledged to let it lie while they developed a voluntary approach, but a lack of improvement in the headline gender pay gap figures, plus the fact that the voluntary scheme has had a very modest take up (and only four companies have actually published figures under the scheme), has led the Government to start the ball rolling for mandatory reporting.
Under a new clause in the Small Business, Enterprise and Employment Bill currently going through Parliament, the Government must bring in regulations (within 12 months after the Bill becomes law) requiring the publication of information showing whether there are differences in the pay of males and females. There are very few details at this stage, apart from the exemption for employers with fewer than 250 employees and a prohibition on requiring reporting more frequently than annually. The Government will presumably have to consult on the details – in particular, on the extent of "pay" information that will have to be disclosed.