The gender pay gap in the UK has been persistent despite the Equal Pay Act 1970. Universities were given a positive duty to redress this in the Equality Act 2010. Some British universities introduced a system of ‘professorial banding’. All professors were regraded from scratch. Surprisingly, this had almost no impact on the gender pay gap. We model how the design of the system could amplify discrimination. With individual data from one research university, we find evidence of gendered external market effects, effects of shorter tenure in the rank of professor and sticky floors.