As even Conservatives now privately concede, Ed Miliband's pledge to freeze energy prices has had more political impact than any announcement since George Osborne's 2007 promise to cut inheritance tax. In the five weeks since the Labour conference, rarely a day has passed without it leading the debate.
If the Tories are hoping to change the subject this week, they're likely to prove disappointed. On Tuesday, representatives of the big six will appear before the energy select committee to be questioned on price rises, and the day hasn't begun well for them. New data  from the energy regulator Ofgem shows that while consumers have been hit by price increases of up to 11.1%, wholesale prices have risen by just 1.7%  over the last year. It's a finding that will make it even harder for the firms to justify their inflation-busting price hikes. While the wholesale element of the average bill has risen from £600 to £610, Ofgem estimates that companies’ average net profit margin has more than doubled from £45 a household to £95.
The big six have responded this morning by disputing Ofgem's figures. A spokesman for British Gas said: "The prices that individual suppliers pay depend on their own hedging strategies, and the Ofgem methodology is, at best, an approximation of what those hedging profiles are. We buy a certain amount of gas more than two years in advance, and if you look at the 24 month figure to October 2013, there has been an 18 per cent increase in the wholesale cost." A spokesman for SSE said: "This is very much a global market and we are seeing increased international competition for supplies, which is putting up prices". But given the consistent lack of transparency shown by firms over how their profits are made, few will be willing to accept their excuses.
For the coalition, the energy companies' kamikaze media strategy is a political headache. While it's likely that George Osborne will announce plans to reduce the green charges paid by consumers when he delivers his Autumn Statement on 4 December, the government still lacks a policy able to convince the public that it is on their side against the big six. A recent poll  by Survation for the Mail on Sunday found that 75% do not believe that green measures are to blame for higher bills. Unless ministers are prepared to demonstrate how they will force companies to return some of their ill-gotten gains, it is alternative proposals, whether Miliband's price freeze or Major's windfall tax, that will continue to dominate.