Hi @TTTT,
As far as I am aware, HMRC VAT Notice 701/49 finance (updated 2019) is the only guidance that HMRC has issued publicly on the VAT treatment of securities trading fees and unfortunately it does not deal specifically with exchange market making fees and rebates.
I know from my Canadian securities law practice that TSX trading fees, including market making fees, are exempt from GST (Canada’s VAT equivalent). This is expressly stated in the TSX Trading Fee Schedule.
I also see that the Irish Revenue authority has issued guidance stating that stock exchange trading and listing fees are generally exempt from VAT but this seems to be broader than UK VAT rules at least insofar as company listing fees are concerned.
Sorry I can’t give you a more specific source for HMRC guidance on the treament of securities market making fees and rebates.