Last week, whilst driving oop norf, I actually saw a motorway electric sign (M40/42 ?) saying 'Keep to the left Unless overtaking'. Much more useful than the usual non-information stuff that appears on these signs.
Hooray - about time too!
http://www.bbc.co.uk/news/business-22770064
It's a shame that these measures aren't extended to spot-fine elderly male drivers who wear hats.