The criticism is of the halfway house first and foremost. If you're going to privatise, do it properly. However, first ask yourself why you're privatising. The big argument that always comes up is competition. Well, you can't have competition on a railway line. Virgin can't compete with GWR because I live in the North West, not the South West. I can't wait for a franchise to run out when I need to make a journey next week. It's a sham. The companies promise some fanciful nonsense and get awarded a contract for 15 years or something, get subsidised up the arse by the taxpayer to pay huge bonuses to some idiot at the top and never deal with any of the real difficulties of running a rail network.
The same is true of energy. It makes no sense to privatise energy companies when energy is fungible and they're all selling the same thing from the same places distributed with the same infrastructure. What value do they add? A different letterhead? It's nonsense.