Cameron and Miliband in Commons clash over energy bills
Ed Miliband has said David Cameron has "no answer" to Labour's pledge to freeze energy prices if it wins power, as the two clashed in the Commons.
The Labour leader said bills had risen by £300 since 2010 and yet the prime minister was still backing "the energy companies not the consumer".
But Mr Cameron called the proposed freeze a "gimmick not a policy".
He suggested Mr Miliband wanted to live in a "Marxist universe" where the state could control market prices.
Labour's pledge to cap energy price rises for 20 months from May 2015, should they be elected, dominated the leaders' exchanges in the first Prime Minister's Questions since their party conferences.
Mr Miliband suggested the prime minister had been left "floundering" by the announcement, arguing it would help 27 million households and nearly two and half million businesses facing rising bills.
In contrast, he said the government's pledge to ensure energy companies put consumers on the lowest tariff would leave 90% of people no better off.
"He says he wants lower prices but prices are going up on his watch. That is the reality," he told MPs.
"We have a cost of living crisis in this country. Energy bills are rising and he supports the energy companies not the consumer. We have a prime minister who always stand up for the wrong people."
But Mr Cameron said energy prices had doubled under Labour and the opposition's support for a target for de-carbonising the energy sector would add another £125 to household bills.
Consumers, he added, would not benefit from Labour's initiative as energy prices would increase before and after the price freeze and the solution was increasing competition in the market.
"I know he would like to live in some sort of Marxist universe where you can control all these things but he needs a basic lesson in economics."
He added: "This is not a policy, it is a gimmick. Of course we all want to see lower energy prices - and we are tackling the cause of high prices."
Earlier on Wednesday, the government announced plans to cap the amount that some regulated rail fares could rise - one of series of initiatives expected in the coming weeks to help families with pressure on their living standards.
The Labour leader said Mr Cameron did not understand an "economic policy is about the cost of living" but the prime minister said Labour's policy to help family finances would lead to higher borrowing, debt and mortgage rates.