EDF Energy today re-launched a flagship tariff which lets customers fix their energy prices for the next two winters without paying an exit fee – but with a “heftier” price tag of £89 more than its predecessor.

Open to both new and existing customers, the Blue+ Promise means people can fix their energy prices until May 2014. The dual fuel bill offers an industry-first ‘Price Promise’ to let customers know if another supplier offers a tariff which works out at £1 a week cheaper.

EDF Energy says more than 750,000 customer accounts have switched to the tariff since April.

Jim Poole, EDF Energy’s Director of Residential Customers said: “As winter approaches, we know many people are worried about what will happen to their energy bills. Customers will benefit from the flexibility of knowing they can leave at any point without paying an exit fee if they find a better deal.”

But the tariff bears a “heftier” price tag which may shock some, according to independent price comparison and switching service uSwitch.com.

Tom Lyon, energy expert at uSwitch.com said: “At £89 a year more, those who missed the boat the first time round will be shocked at the higher price.”

EDF defended the rise by stating its tariff “remains competitively priced”, adding: “We buy our energy for fixed priced tariffs in advance based on the length of the guarantee and the number of customers we estimate will sign up to it. This allows us to offer our customers the best prices we can at the point it is launched.”

However Mr Lyon warned fixed price plans like this should be snapped up in case they end abruptly: “The cost of fixed price plans is creeping upwards. It’s also unusual for consumers to be able to benefit from a price guarantee without an exit penalty. The fact is that these deals will not hang around for long, so consumers need to act now.”

uSwitch says a rival fixed tariff from ScottishPower, the Online Fixed Price Energy March 2014, is £44 a year cheaper at £1,099, although its price protection also ends three months earlier.