Construction of two major gas-fired power plants has been approved by the government.
Progress Power will build a £200M, 299MW plant on a former Second World War airfield near Eye in Suffolk.
Sister firm Hirwaun Power will create a power station with the same cost and power output on the Hirwaun Industrial Estate near Aberdare in Wales.
Both will operate as peaking plants, providing electricity when there is a surge in demand or a drop in supply being generated elsewhere.
Energy minister Lord Bourne said: “Continued investment is essential as we move the UK towards a cleaner energy future. These stations will create jobs while helping to keep people’s lights on.
“Gas is the greenest fossil fuel we have; generating electricity with only half the emissions produced by coal.”
Both plants could be operating by 2019.