An extremely bright Star, which switched on and off. The colour was not unlike landing lights of a plane, to be honest that's what I thought it was except it stayed in the same part of sky for an hour while I drove 80 miles in a truck.

No. The light just went on and off intermittently. When it went out, it seemed to go dim then extinguish, and sometimes it would just vary in brightness. I friend witnessed it from Bristol also. I took into consideration that it may be cloud causing the undulations, but actually when it was bright it actually illuminated some clouds, perhaps as bright as a supernova?

I was driving Southbound on the M5 from Bristol to Newton Abbott, Devon, U.K., and this object was in the south-western sky. When I first noticed it, there was actually a similar bright object in my rear view mirror (wing, driver's side RHS), and as I'd seen 2 police cars going north I thought it was a helicopter searchlight. That one disappeared, but the one in the SW sky remained, albeit going on and off. Can't rule out military craft or some kind of supernova?