This won't work in the UK/Europe. B-RNAV has been a requirement since 11 April 2011 at all ATS controlled routes and levels (previously only above FL95). The only reasonable equipment is a IFR capable panel mounted GPS.

Of course the UK is extra weird because you can fly IFR in class G airspace which is quite extensive outside of terminal areas. More realistically this is VFR in IMC, with the pilot being responsible for his own terrain and traffic separation (somewhere between relying on the "big sky" theory and these days, hopefully, some TCAS system). We even have a special sub-ICAO IR(R) rating which allows a pilot to punch holes in clouds and even to shoot an approach at a airport but not to access the class A TMAs / airways.