Video: Key questions Big Six energy companies must answer In the past month, SSE, British Gas, npower and Scottish Power have all announced price increases, some as high as 10 per cent. "ECO, which is the big one [of the green tariffs] replaced the Carbon Emission Reduction Targets, and what we paid for that on gas and electricity was £52 per year, and that's exactly what's appearing on our bill now, so no, I'm not convinced that green taxes have made such a big difference," she said. Questions have also been raised about whether the Big Six are doing enough to help customers choose the cheapest tariffs. uSwitch recently commissioned YouGov to conduct a poll of over 5,000 people on the subject. Mrs Robinson says less than half of those polled thought that the Big Six had put them on the best tariff. One policy to tackle rising energy costs was put forward last month by Labour leader Ed Miliband - a 20 month freeze on gas and electricity bills if Labour win the 2015 general election. Critics described the policy as "populist gimmickry" and "economically illiterate" and energy companies claimed it could lead to energy shortages and even blackouts. Mrs Robinson says such a freeze could have "a significant impact towards the end of the decade" on crucial investment by the energy companies, even if blackouts don't happen in the the short term. I think the companies do have a real point here. We do need to invest in new generation and if there's a prize freeze being threatened I don't think they're going to make that investment," she said.