Vice has an interview with the two creators:
In 2017, the UK government made it compulsory for all companies with 250 employees and over to report the difference in earnings between men and women. Anyone can look up the data on a government site, but [the creators] saw a chance to bring the information to a wider light.
...
More positively, the Gender Pay Gap Bot has highlighted some companies that pay women and men equally, and occasionally even a few with a slightly higher pay for women than men, like the London Fire Brigade
Oh, and if anyone wants to verify the data, it's all here: https://t.co/sJQcFvDhQ7
— Francesca - copywriter (@franwritescopy) March 9, 2022