I have to second Jo's comments, I think close passes are probably the most discouraging thing about cycling. Having motor vehicles zoom past at close distance is threatening and unpleasant. I suspect it puts more bikes back in the shed than anything else, and is also why a lot of people cycle on the pavements. I'm an experienced cyclist but there's a section of my route that I'll generally avoid because I know – no matter what I do – that there'll be a unpleasantly close and potentially dangerous pass.
I think many drivers simply don't realise it – you get exactly the same behaviour walking on lanes, cars fly by, often without giving an inch or slowing for a second. They have no concept I suppose of being that close to passing traffic, presumably because they're always sitting inside of it. Of course, and there are the aggressive bullies too.
I'm not optimistic of small, local campaigns like this. We need proper road policing that goes beyond reading number plates. That requires a significant re-evaluation of how we police the roads and ultimately our relationship with our motor vehicles.