Energy supplier and generator E.On has cut UK household gas bills amid criticism of the industry following oil price falls.
Germany's E.On said on Wednesday it was reducing bills by 5.1%, or £32 off the average annual bill.
Companies have faced criticism from UK energy regulator Ofgem and the government that retail price cuts have not kept up with falls in the wholesale price of gas.
It was the first time in six months that any of the big six energy firms have cut their prices, according to the BBC.
Ofgem chief executive Dermot Nolan said: "We have consistently called on suppliers to explain why retail prices are not falling and this price cut goes some way towards addressing that challenge."
But, given the fact that a price rise by one supplier often triggers immediate increases by rivals, some questioned whether other suppliers will be as quick to follow E.On in cutting bills.
As well as E.On, the UK's "big six" major suppliers include Centrica (LON:CNA), EDF Energy (EPA:EDF), RWE-owned Npower (ETR:RWE), Iberdrola-owned Scottish Power (BME:IBE) and SSE (LON:SSE).
Other smaller suppliers such as Ovo Energy have been encouraged to enter the UK market to provide more competition for the established providers.
Director of consumer policy at price comparison website Uswitch, Ann Robinson, said: "Wholesale electricity costs fell 23% last year, so why have we not seen a single reduction to big six standard electricity tariffs?
"This is yet further evidence that the energy market simply is not working for most UK households.
"With wholesale prices predicted to remain low this year, consumers should be seeing bill reductions of at least 10% – around £120 a year – on both gas and electricity.
"Now is the time for the other major suppliers to step up to the plate and offer decent, double-digit reductions."