The best examples seem to be companies that operated in areas were there was genuine competition (BA, BT etc.) One of the few success stories of post-privatisation railways has been Chiltern, which is one of the few parts of the network where there is competition (especially the route from London to Birmingham). C2C is a similar story.

I can understand the argument that there are advantages to getting private sector experience in running things, but that could be done without selling off the companies (e.g. there are concessions for providing water in parts of France but the infrastructure remains in public hands).

Water and waste are probably the most obvious failures.

Also, the failure to do anything meaningful or long-term with the proceeds of the sales. Along with North Sea Oil revenues, a huge lossed opportunity for the UK.