Prices for SSE's household customers in the UK are to increase on average by nine per cent for both electricity and gas from the middle of October.The company, which also trades as Scottish Hydro and Swalec, said five million electricity customers and 3.4 million gas customers would be affected by the hike.It blamed the rise on increases in the cost of using the electricity and gas networks, as well as the costs of the government's green energy schemes.It also said the average cost of gas for the coming winter on the wholesale energy markets was around 14% higher than it was for last winter.However, the company committed to capping household energy prices at the new level until at least the second half of 2013.Chief Executive Ian Marchant, called the forthcoming increases regrettable but unavoidable."We pledged last summer to cap our energy prices for as long as possible and until at least August 2012, and then in January extended this pledge to October 2012," he said."Unfortunately, the increases in costs that we have seen since making this pledge can no longer be absorbed and mean that we are unable to keep prices at their current levels beyond this autumn."But consumer groups reacted angrily to the announcement."We can't go through another winter with people worrying about their energy bills, the Government and the regulator must reform our broken energy market," said Which? executive director, Richard Lloyd."It's time for energy prices to be properly transparent and tariffs to be made simpler, so that consumers get a fair deal."Earlier this year all of the 'big six' energy suppliers made small cuts to either gas or electricity bills.It is expected that the remaining five firms will soon follow in SSE's footsteps by raising bills again.