I don't know which rules are most commonly broken, but one that blows me away on the country road leading to home is the amount of people cutting blind corners. I've seen one big crash and a few very close calls in the 2.5 years I've lived up there, it's insane. But yes the failing to keep left in general seems to be a common thing, but failing to indicate and follow basic give way rules (if you pull out infront of someone and they have to so much as touch their brakes to not crash into you, you've failed to give way. Some people seem to say "oh well they were going too fast" as they spend the next 500m getting up to the speed limit - much to the detriment of the 5 cars that are now backing up behind them).
Oh and something that's far too common (but seems relatively local to Silverdale) is peole turning right at a roundabout that don't indicate at all, have had a couple of closeish calls because they're quite small roundabouts here.
If people just applied a bit of common sense and ditched the "he has brakes, he should use them if he doesn't want to hit me" attitude (something that I REALLY notice when driving the Escort because it's not as manouverable as modern cars to avoid these people) then I reckon road accidents would halve overnight.
