The Cabinet Office runs data-matching every two years to catch duplicate payments, pensions still paid to the deceased, and fraudulent claims — literally "money paid that shouldn't have been". Caveat that matters: only national totals are public; per-council results sit in a secure portal, so this dataset cannot support per-council ranking without a bespoke collection (committee-paper scrape or a PSFA data request).
Sourcing details, files and caveats: SOURCE.md.
Variables this dataset yields: VARIABLES.md · browse variables/.