@SimonJI think I may have found a workaround for your issue that you can try.
Setting the system property -Daws.region=UK should override the region used by the S3 plugin I think (disclaimer: I did not try this out, but it seems likely to work).
Fair question. So far I have not seen this come up. This may be a result of simply no one having tried using a different region yet. I will investigate this and update here.