I'd only worry if you were flying in the gulf region (!) with non Mil kit. It's possible to regionally degrade the signal.
See:
http://clinton4.nara.gov/WH/EOP/OSTP/html/0053_2.html
Additionally, we have demonstrated the capability to selectively deny GPS signals on a regional basis when our national security is threatened.
As for a £90 garmin, buy it in / from the us and update the firmware to the UK / Europe verosion. :0