The UK’s ‘big six’ energy providers are charging some customers up to £200 if they switch tariff before their fixed rate period has ended, according to consumer watchdog Which?

And Which? also claims that some customers who are nearing the end of their contracts are sometimes “rolled over” to another fixed deal if the energy company does not hear from them before the contract ends.

A survey by Which? found that in terms of early exit fees, EDF’s fixed price 2015 tariff carries the highest penalty for switching, with dual fuel customers charged up to £200 for exiting early.

However EDF has stressed that customers would not be automatically rolled onto this tariff.

The supplier’s shorter-term fixed-price tariffs have an early cancellation charge of £50 for dual fuel, and EDF gives customers 30 days to switch from the new tariff without penalty.

Early exit charges for cancelling fixed-price dual fuel tariffs from other suppliers cost up to £100 with British Gas, up to £75 with Scottish & Southern Energy and up to £50 with Scottish Power.

Npower and E.ON do not roll on customers to fixed-price tariffs with cancellation charges.

Chris Eagle, commercial manager at Energychoices.co.uk, said: “This is a trap that people really should be aware of. If you are on a fixed rate deal, make sure you know when it comes to an end and switch accordingly.

“If you forget to do this in time, you will either end up stuck on a tariff that may not suit you and find yourself spending hundreds of pounds to get out of it.

“This is yet another reason to compare energy prices and tariffs on a regular basis, and make sure you switch as and when is necessary.”