Just been on a speed awareness course and can concur with funkymonkey and hairychested. #
I also learnt (yesterday) that the national speed limit is 60mph (always thought it was 50mph), unless there is a central barrier between you and oncoming traffic, the NSL then becomes 70mph.
I used to think this was common knowledge, but then when I tootle past people on derestricted sections of dual carriageway, I think a lot of people still think it is 60mph, as the average speed of other drivers is generally slower than motorways etc.
At the other end of the spectrum, some drivers seem to think that an overtaking lane is a 70mph derestricted area. The A9 is a good example of this, as people fly up and down the overtaking lanes.