I think this is a very bad idea...
http://news.bbc.co.uk/2/hi/uk_news/england/west_midlands/5337292.stm
http://news.bbc.co.uk/2/hi/uk_news/england/west_midlands/5337292.stm
Generally this seems to run pretty well, but one broken down vehicle can cause everything to grind to a halt. A car stopped in the hard shoulder...caused big tailbacks. Everything in the hard shoulder lane (generally lorries) had to overtake the car. The situation seems dangerous, but the actual traffic speed is low during the peak periods anyway (so much for unrestricted motorway speeds), so it isn't quite as bad as it seems.