Households that want to switch energy tariff can register with Which? as the lobby group has promised to negotiate a collective deal for consumers.
The campaign, called The Big Switch, aims to help households get a better gas and electricity deal as Which? estimates consumers collectively pay £4.1 billion a year more than they need to by not switching to the cheapest deal.
Regulator Ofgem says six out of ten people have never switched. Those on their standard tariff are almost certainly paying too much as the best deals are reserved for online customers.
How it works
Which? is inviting all energy suppliers to take part. It will negotiate with them to secure the cheapest deal for all consumers who join by 31 March.
Firms will be invited to submit a deal and take part in a reverse auction. The winning deal will be offered to everyone who signed up, and they will get a personalised savings estimate.
It may be that consumers in one area are offered a different deal to those in another area, given energy prices can vary wildly depending on location.
Which? will handle the switching process.
If you register, there is no commitment to sign-up with the new supplier so you can always pull out.
How to register
You can sign up online at www.whichbigswitch.co.uk but must do so by 31 March.
What happens after
Once Which? has secured a deal, it will notify those who've registered of the outcome and they can choose whether or not to accept it.
Martin Lewis, MoneySavingExpert.com creator, says: "This is interesting and good to see Which? at the vanguard of collective switching. As blogged yesterday, MoneySavingExpert is also considering a slightly different form of collective switching see my Call from Ed Davey blog.
"It is intriguing to see how well Which? can do with this. My worry is that unless the product is cheaper than the market cheapest, which I hope it will be, there is little benefit for the consumer compared to going direct to a comparison site, as effectively it's just negotiating a one-off bulk deal.
"That will be the crucial test but it's still a good idea to sign up to find out.
"My hunch is the critical mass for collective switching will be a long term model where the consumer joins a group that provides long term cheap prices without the need to keep re-committing.
"In other words, rather than being an energy tart, it provides a long term stable relationship with consistently cheap prices, though not market leading. According to polls we've done, it's this simplified system people want."