What the NPAS scheme involves is reducing the number of aircraft and the number of pilots required to fly them, as a matter of policy. I don't think that TUPE prevents people being made redundant when "the demands of the service" "require" a reduced service and fewer employees.
Sadly it seems to me that some pilots currently employed as police pilots will inevitably end up losing their jobs. Which pilots is another question. I don't see any persuasive argument for direct-employed pilots being in a different position from contractor-employed. NPAS seem to have said little, but if a national organisation is to run air support the individual police forces will no longer be providing the service themselves. So those pilots employed by the police force and the contractor company are essentially in the same position, aren't they? Their employer is no longer providing air support.
[The same probably is not true of sub-30 year police officers because they are not normal employees (in an employment sense)].