PFI - "Progressive Functional Implementation"
ATC speak for, 'we haven't proven the system' reliably, but we're running out of time and will go 'live' regardless of ATCO under confidence!
There's been at least one other 'reversion', but kept in house.
The pilots, flying public, operational ATCO's deserve better, than an in house denial and suppression of the facts.
An external and independent assessment is required! Urgently!