Nick Clegg announces rules for power firms to promote cheapest tariffs along with green deal to encourage energy-saving
Consumers will be told once a year by their energy company if they could be on a cheaper tariff, so saving them up to £100 a year, Nick Clegg, the deputy prime minister will announce.
It is the first time the "big six" energy companies will be required to send such information to their consumers, including how they can switch to a cheaper tariff.
In a major speech on the future of green energy in the UK, Clegg will also deliver a rebuke to his Conservative coalition partners for suggesting Britain need not show a leadership role in Europe.
He will also try to combat claims that action on climate change is an unaffordable luxury at a time of recession. Clegg will argue that "lean times can be green times too".
Green campaigners have been on the back foot since the leak of an internal report for the prime minister into the cost of the coalition's green energy policies, claiming consumers could see £300 a year added to their bills.
Clegg will announce the big six energy companies – EDF, E.ON, British Gas, Southern, Scottish Power and npower, which supply 99% of British homes with energy – will from autumn be required to write to customers every year to tell them their best tariff and how to get it. A million vulnerable customers, such as pensioners and those assisted by the warm home discount scheme, will be contacted twice a year.
Customers will also be offered the best tariff if their contract comes to an end and if they contact their supplier at any time to ask.
It is claimed that currently seven out of 10 people are not on the best available tariff, yet show little capacity to switch. In 2010, 75% of people did not change their tariff.
Consumer Focus will welcome the measures, but warn one-off mail shots have to be part of a wider strategy to make energy firms regain customer trust.
In his speech in Canary Wharf, Clegg will also announce he is working with energy companies to put special barcodes on energy bills so that a smartphone will be able to get quotes and switch tariff or supplier in a matter of minutes.
Clegg will also acknowledge tough economic times have put some voters off green policies. He will say: "While sceptics say that it's all too difficult at a time of deep fiscal consolidation, and that economic uncertainty poses too many challenges, I say periods of economic reinvention force us to do things differently. I say that lean times can be green times too.
"We are undergoing a profound transformation within our economy. And for the first time ever our economic and environmental mantras are exactly the same: waste not, want not.
"Whether it's waste of energy, waste of money, waste of our potential, we are focused on conserving our precious resources … Responsibility, sustainability are the watchwords of the day. And that creates a unique opportunity to put environmental thrift into the mainstream".
He will admit more work has to be done to remove "the hassle factor" that put consumers off reducing their home energy consumption.
He will point to the way B&Q is offering in conjunction with local councils to clear someone's loft while installing insulation, an offer that greatly increased willingness to take up the switch.
He will also highlight the government's plan from the summer to trial a project with First Utility and America's Opower, where consumers are told how much energy similar households use in their locality. Opower has reduced bills by 2% in the US by showing consumers how neighbours are doing better than them.
He will also insist the government had arranged the green deal, due to begin in the autumn, so that businesses and homeowners can introduce energy-saving home improvements at no cost upfront.
"Customers will have energy-saving measures installed in their homes by trusted suppliers, from high street brands to local traders. However, they will only begin paying for those improvements once they are complete. Payment will be made through their bills over a period of time, and they shouldn't be out of pocket because their homes will be more energy efficient, allowing them to save on their energy bills each month," Clegg will say.
The government is already planning to give the energy regulator Ofgem powers to direct the energy companies to compensate overcharged consumers.
• Use the Guardian's energy switching service to see if you could save money