David Cameron is behaving in a “pretty disreputable” way over the proposed UK television election debates, Ed Miliband has said as he confirmed that he would be prepared to take part in an “empty chair” debate without the prime minister.

The Labour leader accused the prime minister of running scared after Cameron said that he was minded not to take part in the three planned television debates unless the Green party is included.

Tory strategists have said in private they want to use the Greens as an excuse to avoid the debates taking place amid fears that they would boost the Ukip leader, Nigel Farage.

The Labour leader criticised the prime minister during an interview on the Andrew Marr Show on BBC1 in which he also:

• Challenged the Tories and the Liberal Democrats to support Labour when it holds a Commons vote this week that would force energy companies to pass on price reductions in the wholesale price of oil and gas to consumers.

• Accused George Osborne of planning to hold a “gimmick” vote in the House of Commons on Tuesday when MPs will be asked to support the Tories’ deficit reduction plans. The Labour leader said that he would vote with the government but would stand by Labour’s own deficit reduction plan.

Miliband criticised the prime minister after he said last week that he would not take part in the three planned television election debates unless the Greens were included. The chances of the Green party securing a place in at least one of the debates diminished on Thursday when Ofcom, the commercial television regulator, suggested in a consultation document that it is unlikely to qualify as a major party. The three main parties, plus Ukip, would qualify as major parties.

The Labour leader said of the prime minister’s response: “It is pretty disreputable that David Cameron went in to the 2010 election saying these debates were the most important thing that we could possibly have, people shouldn’t make feeble excuses to get out of them and he is doing precisely that. He is running scared from these debates.”

Miliband said the debates should still take place even without the prime minister whose absence could be marked by a chair in a process known by broadcasters as “empty chairing”. He said: “I want these debates to happen, I think they should happen with David Cameron or without David Cameron. In the end that is a matter for the broadcasters. But I don’t think any one political leader should be able to stop these debates happening, should be able to veto these debates, block these debates. I want them to happen.”

Asked whether he would still take part without Cameron, Miliband said: “Absolutely. If an empty chair represents David Cameron in these debates, so be it. These debates need to happen. They are owned by the British people, not owned by David Cameron or by anybody else. They should happen. Frankly the prime minister should stop ducking and weaving and trying to avoid these debates.”

In his main political announcement of his interview, Miliband announced that he would build on his pledge to freeze the price of fuel bills until 2017 by forcing energy companies to cut bills when the wholesale price of energy falls. Labour will hold a Commons vote this week to allow the energy regulator the power to cut retail prices when the wholesale reductions are not passed to consumers.

He said: “We are going to bring before the House of Commons a vote in parliament to say the government should bring forward fast-track legislation to ensure that we give the regulator that power. We’ve seen wholesale costs go down 20% in gas prices over the last year and no reductions in bills. We would give the regulator the power to cut prices, to give consumers immediate relief.”

Osborne tweeted last week that the government would put pressure on energy companies to pass on the cut in wholesale prices. But Labour believes that legislation is the only way of forcing change.

Miliband also had the chancellor in his sights when he dismissed as a “gimmick” Osborne’s plans to hold a Commons vote on Tuesday on the Tories’ deficit reduction plans. The Labour leader said he would support the government, as the party seeks to avoid accusations that it is failing to acknowledge the significance of the deficit.

Labour believes it can laugh off the vote because it is a government measure which means the wording is likely to be limited to the agreed coalition position. This covers two broad areas: spending plans for 2015-16, which have already been endorsed by Labour, and broad plans to eliminate the structural budget deficit by 2018. But the Lib Dems agreed with Labour that the fiscal consolidation should be achieved both by spending cuts and tax increases. The Tories believe it should only be achieved by spending reductions.

The Tories plan to start running a surplus from 2018. Labour has pledged to cut the deficit in every year of the next parliament but has avoided setting an arbitrary demand for the elimination of the structural deficit to avoid sucking demand out of the economy.