Energy customers signed up to Big Switch, the collective bargaining campaign run by Which?, are still missing out on the most competitive deal.
Co-operative Energy is to roll out a fixed-rate deal to Big Switch members but it's not the cheapest deal on the market and will only be available to 30,000 of around 280,000 customers who signed up to the campaign.
Those who succeed in getting the Co-op deal, on a first-come, first-serve basis, will be charged between £1,048 and £1,144 per year for their energy, depending on how they pay.
But the cheapest deal on the market comes from First Utility at £1,027 a year.
"The Big Switch was a brave and bold move, but the outcome is disappointing," says Ann Robinson, director of consumer policy for uSwitch.com.
However, Robinson is pleased to see that a smaller supplier has put forward an attractive deal to those signed up to the campaign, even if it isn't the cheapest in the market.
"This will help to encourage more consumers to realise that the smaller players are a serious and viable alternative to the Big Six suppliers that currently dominate the market," she adds.
The Big Switch campaign worked by Which? getting households to sign a petition demanding cheaper energy bills. It then approached all the energy suppliers with the petition and asked them for their best energy deal. The supplier with the most competitive tariff would win and Which? then switches all the householders to the new improved deal (though this is not compulsory).
Five other energy companies, EDF Energy, E.on, First Utility and Scottish Power are signed up to the campaign, along with Co-op.