From the CAA document:
In the short to medium term ground-based augmentation systems (GBAS), aircraftbased augmentation systems (ABAS), space-based augmentation systems (SBAS)
and augmentation with stand-alone GNSS such as Galileo offer the possibility to achieve the RNP. This study has shown that GPS augmented with Galileo offers a user level monitoring capability through RAIM good enough to satisfy the integrity
requirements for en-route to precision approach phases of flight.
So there it is: GPS might be good enough for the FAA (and others), but we Europeans obviously know better and will stick with medium wave radios until we have our own toy that we can charge our users for.