Energy suppliers must bring in simpler tariffs by the end of the year, regulator Ofgem has warned.
Suppliers are to offer no more than four core tariffs per fuel to avoid unnecessary confusion.
They must also inform customers of the cheapest offers available, personalised for individual consumers on all their bills and annual statements – but this will come into force at the end of March 2014.
In the shorter-term, from this week, suppliers must also follow strict new standards of conduct in all their interactions with consumers, from when they are marketing energy deals to them, to making amends when customers make a complaint about any aspect of their energy supply.
Failure to meet the required standards will result in fines.
The new rules, which can now be enforced, mark the first stage of Ofgem's reforms to make the energy market "simpler, clearer and fairer".
It has warned energy suppliers to deal with all customers in an honest, transparent and professional manner, as well as providing information clearly in jargon-free language.
Andrew Wright, Ofgem's chief executive, said: "Suppliers have already taken some steps to make the energy market simpler for customers and we welcome that, but our package of reforms means they must go further…
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"They have to make sure they are embedding simplicity, clarity and fairness into all their dealings with consumers to tackle the lack of trust that has blighted the market. The standards of conduct will also enhance consumer protection as they are backed by Ofgem's power to levy fines."
Ann Robinson, director of consumer policy at uSwitch.com, added: "This news from Ofgem is welcome. Moving ahead with standards of conduct based on a set of principles is a move away from more detailed regulation which sometimes can fail to deliver the intent and should mean that consumers in the future will get a more comprehensive and better overall service.
"Because these standards are at a high level, energy companies will be worried about translating them into practises which Ofgem will consider acceptable. This is of particular concern because of the emphasis Ofgem have placed on using fines when standards have not been met."