By Daniel Hunter
The government will, today (Tuesday), set out their plans to ensure that energy firms offer customers the lowest suitable tariff.
Energy Secretary Ed Davey will set out plans for fulfilling the PM's pledge last month to bring in legislation.
Davey will say that all energy companies must reduce the number of tariffs they offer for gas and electricity to four each.
However, consumer groups and energy firms warned it could mean some of the cheapest tariffs on offer disappear.
Cameron's pledge came as something of a shock last month, and Labour will now be very keen to ensure he follows through with it.
"We will be legislating so that energy companies have to give the lowest tariff to their customers," Cameron said.
Labour welcomed plans to make tariffs simpler, but said the government also needed to reform the energy market and create a new watchdog to force companies to pass on price cuts.