It's too late to change now. Think about every single sign post, every single line marking on the road, the insurance would sky rocket, death counts would go up... it just has a snowball effect. The costs would be so high, and for what? So we can be the same as most other countries.... blergh, would never happen. We barely/don't have enough money to keep our roads in decent condition, never mind considering to change Don't get me wrong, I'd love it to though, would make things hell of a lot easier.
In my opinion the driving on the left makes a holiday in the UK a little bit more special. Implementing the metric system doesn't cost that much though.
Well changing "cold-turkey" with everything happening at once wouldn't work anyway. You have to make slow changes. Let people adapt. Change everything over the course of 10 years or so. Costs would be very doable that way.