Robert, slow driving in Scotland is either due to two reasons:
1. Tourists pootling along looking at the view rather than driving to get somewhere, or more likely,
2. Scottish locals being too tight to drive fast and do less mpg :-)
Although speaking as a cyclist, I wish people did drive more slowly along country roads because there's precious little space if a car comes round a blind bend too quickly and there's a cyclist. Things have improved a lot in the UK since Brad Wiggins won the Tour de France and a load more people got on their bikes - there's had to be a greater awareness of cyclists by drivers since there are so many more on the road these days.