What BoE can say is that certain risks are unacceptable for UK banks, period. It's not BoE shopping for data centers, it would be BoE setting the rules for ever

What BoE can say is that certain risks are unacceptable for UK banks, period. It's not BoE shopping for data centers, it would be BoE setting the rules for every bank shopping for data centers. If BoE does not like some risk that really does come with the territory and everybody who uses public cloud is subject to that risk, oh well, then that would imply that UK banks have to keep out of that territory and can't use public cloud for their key services - it is a bit drastic, but certainly something that BoE has the right to rule if it really wanted. On the other hand, if there's a way to use public cloud and meet the requirements, but current major vendors are simply not offering it, then BoE can make up arbitrary requirements, followed by the major UK banks going to the major cloud vendors with a proposal "meet these requirements or we won't use your services, because we'd be prohibited to".