The Equality Act (Gender Pay Gap Information) Regulations 2016.

Gender Pay Gap reporting regulations will come into force in October 2016, with organisations of 250 or more employees having to report in April 2017.
Draft Regulations now published are open for consultation until 11th March – but on first read they seem relatively straightforward and should be of immediate assistance to firms in identifying whether they have an equal pay issue and how it might be addressed.
There are some simple (median / mean / quartile) calculations to complete- but clear guidance is given.
A Company pay report will have to be published on a readily accessible website each year, and the information also has to be passed directly to the government.  Subject to consultation, the intention is for employers who do not comply to be identified publically and penalties for non-compliance may be introduced.