Ed Matthew, director of the Energy Bill Revolution (EBR), a group of businesses, trade unions and environmental campaign groups, said: "Simplifying tariffs and moving consumers to the cheapest is a no-brainer.
"But no-one should kid themselves this will bring down energy bills overall. The main benefit is really to make life less confusing for energy consumers.
"The danger is that it distracts attention from the only real, long term solution to high energy bills which is to make every UK home highly energy efficient.
"From next year, the Government will rake in over £2 billion in carbon tax, rising to £4 billion by 2020.
"If this was recycled back to households to make homes super insulated, it would be enough to end fuel poverty and in time slash the energy bill of every home in the UK."
It is possible that some of the best deals on the market will disappear. We could lurch from a minefield of deals to virtually none at all.
Downing Street sources are adamant tomorrow's energy bills announcement will stick to David Cameron's promise of lower tariffs, but will it?
Ministers are poised to announce plans to decrease energy bills in a bid to get customers on the lowest tariffs available.