At present, the UK NATS internal flight data processing system only looks in FPLs for 8.33 and RVSM equippage, and then only when relevant to the airspace where it is required. Everything else is left to the pilot to ensure the equippage requirements are being met.
Not to say that Mode S 'warnings' might not become a requirement within the NATS kit in the future but it is not looked for at the moment.