The EAT (Lady Smith presiding) has held that red-circling of an individual's pay following a TUPE transfer will normally be a genuine material factor justifying a disparity in pay between a man and a woman.
That much is uncontroversial. But the EAT also held that an employer is under no duty to 'narrow the pay gap' after the transfer, for example by freezing the salary of the transferred employee(s) until others have caught up and equalised. Provided the decision to award everyone pay rises (and thus perpetuate the pay gap) is not tainted by sex, the employer will still be able to establish a defence to an equal pay claim.
This is a nice, clear judgment on a tricky area of the law. Paragraphs 37-39 are the ones to read.
Skills Development Scotland v Buchanan.