Well, at least Ed is consistent. When he was at DECC he was also touting equally unworkable plans to control energy prices. Milliband has picked up on a view that Energy companies are all overcharging (a view espoused by Ofgem too) - however it isn't at all clear that that really is the case and the energy companies are strongly in dispute of this fact therefore they won't be cooperative with a policy that essentially means the would have to admit that they have been overcharging.
The government needs to realise that it has to provide a workable framework for investment and be prepared to underwrite risks for what are essentially major infrastructure projects. Whilst there is no certainty around policy and government backing risks just increase and prices follow suit. We need a government that will overtly support renewal of the nuclear fleet as well as a concerted effort to support responsible fracking activities.