FPS is the UK's domestic real-time-payments rail, operated by Pay.UK and settled at the Bank of England. The rail runs 24/7 with a per-transaction cap (currently £1m for most participants). The legacy message format is an ISO 8583-derived schema; the New Payments Architecture (NPA) migrates the rail onto ISO 20022 pacs.008 + pacs.002 over the 2025–2027 window.
The migration is *rail-internal* — the customer-facing pain.001 / pain.002 layer that iso-compliant covers is unchanged. What changes is the bank-side translation between pain.001 and the inter-bank pacs.008 + scheme-specific overlays.
UK Faster Payments is one of the planned Phase-3 scopes for iso-compliant. The relevant rule-pack overlay is the FPS-specific structured-address requirement (slightly different from CBPR+ in timing) and the UK Confirmation-of-Payee (CoP) integration.