Decided to remove UAT. In order to do this we deactivated users from UAT to see what noise was created (none). Then we adjusted the TIS UAT→NDW UAT ETL to be a TIS Stage→NDW UAT ETL - this way any impact of changes we're pushing through on NDW are more likely* to get surfaced in advance of them appearing on NDW Prod. Then we switched off Stage. Finally we set up a scheduled data sync from TIS Prod→TIS Stage (every weekend - our of working hours, enabling multi-day data tests to be carried out during a working week (but not spanning multiple working weeks).
*not always: in the case of code going up to Stage, approved on Stage and released to Prod within one day, and; in the case of rogue code passing existing tests but erroring because of a missing test
Background
UAT was set up as a temporary pre-Prod environment before we went live, as a training ground for new TIS users.