Which doesn’t apply in the UK post Brexit, hence this situation. The UK could cram down interchange fees (such that the EU had) with their own regulation if they don’t want merchants banning rent seeking payment networks.
The whole point of brexit was to get rid of the sort of fair, efficient, reasonable legislation the EU pushes. Brits want to be fucked over by big US mega corps and are tired of the EU refusing them that right. As a Brit I wish it wasn't true but here we are.