"Somebody's got to call time on a market that is not working," Ed Miliband told ITV News political editor Tom Bradby today, speaking about his plans to tackle household energy prices.
The Labour leader said a two-year price freeze would allow a Government to "get in place a new regulator who can do precisely what the current regular can't - which is when wholesale price reductions aren't passed on, cut people's prices."
As Ed Miliband clashes with the energy giants on prices, it is worth knowing how your expensive energy bills are actually made up.
A leading competition lawyer says an energy price freeze could leave Labour open to challenges from the courts or the European Commission.
Whether or not you approve of a state intervention into industry, there are at least two big potential obstacles for an energy price freeze.