Sheldon Mills, the executive director for consumers and competition at the Financial Conduct Authority (FCA), worked on board membership rules which would have allowed companies to define a woman as anyone who identifies as female.
Mr Mills was appointed to his role at the FCA in March 2020, a month before he became chairman of Stonewall where he had been a trustee since 2013.
The proposals on self-identification, drawn up in 2021, would have applied to the boards and committees of all companies listed on the London Stock Exchange.
However they were watered down following a public consultation which received more than 400 responses on the issue of self-identification.