The UK's biggest energy providers have done a deal with the government that will see them write to customers every year to tell them what their best tariff is and how to get it.The six firms, EDF, E.On, British Gas, Southern, Scottish Power and NPower, supply 99% of British homes with energy.They have come under fire recently for making their tariffs too complicated.The government says that there are more than 120 different energy tariffs, with seven out of 10 people currently not on the best deal for them. It wants to encourage more people to consider switching, saying that in 2010, 75% of people did not change their tariff.In a speech later today, excerpts of which have been released already, Deputy Prime Minister Nick Clegg will announce that the plan will be effective as of this Autumn.If consumers call their providers, firms will have to offer them the best deal as well."We're also working with energy companies to put special barcodes on energy bills," he will say. "You'll be able to scan them with your smartphone to get quotes and switch tariff or supplier in a matter of minutes."Audrey Gallagher, Director of Energy at Consumer Focus, said the move was long overdue. "But this is probably only going to work if this is part of a much wider strategy to really help people engage more effectively with their energy bills, really cut their costs and get the best out of the energy market," she said.