New Ofgem rules came into force today which stop energy firms from raising prices on fixed-term contracts.
Companies are also banned from automatically rolling customers onto new fixed-term deals when their current one comes to an end.
The regulations are the latest stage of Ofgem's reforms to "reset the energy market", making "a positive difference for consumers".
Ofgem's review found that a lot of fixed-term offers could still see consumers tied into tariffs they couldn't get out of. It also identified fixed-term deals that included termination fees which meant customers missed an opportunity to compare the market.
The regulator is ensuring that prices and conditions agreed to when signing up will not be altered, with roll-overs being replaced by a tariff that allows switching without penalty. Consumers will also get 40 days warning that their fixed deal is coming to an end.
"Ofgem is going to make it easier for consumers to 'vote with their feet'", said chief executive Andrew Wright. "Our reforms seek to give consumers the tools they need to find the best energy deal for them."
Ofgem's next reformatory step is the introduction of simpler tariffs by the end of December 2013. This will see all tariffs having a standing charge and single unit rate, with suppliers limited to offering up to four "core" tariffs per fuel (for electricity and gas).