As far as I know alot of the Orkney Islander stuff is done "VFR". The Advisory routes are used by the Shorts 360s, Twotters, Jet Streams and SAABs (no oxygen but I am not sure if they are pressurised) in Northern Scotland. Most operations seem to stay below FL150.
As a helicopter pilot, we never go airways (too high) so its class G IFR, very often routing direct (airspace and terrain permitting). But then again, we are not scheduled.
IO540, I am intrigued by your comment that IFR means Eurocontrol. Perhaps I have been lucky in that all my IFR has been in the North Sea system, or in areas where traffic densities are so low, we have always been able to file IFR over the radio (VFR - IFR flights). I have only ever filled out one IFR flight plan!