A five-year price freeze is due to end for 460,000 British Gas customers, leaving them in a bind as to what to do next.
After signing up to a five-year fix in 2005, Price Protection customers have been paying as much as £473 a year less for their energy, according to comparison site uSwitch.com, but this is due to end on 30 April.
Fixing their bills over this period meant they avoided huge price hikes in 2006 and 2008. As a result, they paid on average £4,100 for their energy over the past five years, compared to standard plan customers who faced average bills of £5,253.
"Everything fell into place for this group of customers. They fixed at the right time, for the right price and for the right length of time," says Tom Lyon, energy expert at uSwitch.
Once these deals have finished, customers face a difficult decision as to whether to fix again. Not all customers coming off fixed-price plans fare so well. Many end up paying more because they miss any price drops.
"This shows how hard it is to get it right so we would always urge consumers to think carefully before signing up for a fixed-price plan," says Mr Lyon.
Online plans generally offer the most competitive rates, but consumers will need to switch regularly and could face early exit penalties.