Catia,
This is not correct, there is no need for GNSS to meet RNAV-1, infact if you look at a LIDO chart it is endorsed by the ANSP as "RNAV-1, DME/DME,IRU or GNSS required"
You should also note that RNAV-1 and European P-RNAV are although similar not the same thing.
PT6A
P-RNAV is a European Navigation Standard, which equates to a track keeping accuracy of +/-1nm on SIDs, STARs and Initial Approaches for 95% of flight time. It requires the procedures to be coded into a navigation database and used without modification by the flight crew, other than ‘direct to' ATC clearances. It also includes the need for ‘fly-by' and ‘fly-over' waypoints. Whilst the procedures are designed to a +/- 1nm tolerance, track keeping is based on air navigation service provider assessment of the available navigation aids against the minimum airborne equipment standard. There is no requirement for RNP alerting functions within the FMS and track keeping can be assumed to be met on the condition that airborne equipment and radio updating are functioning correctly, the aircraft is being flown with Autopilot or Flight Director and navigation cross check has been completed at the start of the procedure as defined in the aircraft operations manual. P-RNAV approval covers SIDs and arrival procedures only to the Final Approach Fix (FAF). P-RNAV was primarily intended to be a Terminal Area navigation specification, however some European air navigation service providers are also intending to specify use of P-RNAV in the continental en-route structure to provide greater capacity with closer route spacing. P-RNAV will not be a navigation specification in the PBN since it allows the use of DME/VOR updating which the equivalent RNAV1 in the PBN manual does not. Furthermore for RNAV1 SID's there is a requirement for RNAV guidance no later than 500 ft above airfield elevation which some current P-RNAV approved aircraft do not meet.