Scottish & Southern Energy (S&SE) is putting up its gas and electricity prices for the second time this year.
No more increases this year promises S&SE
From 1 May, its domestic customers will see their gas bills rise by 16.5% and electricity bills by 9.4%.
In common with all other energy suppliers, who have also put up their prices, the company blamed the high wholesale cost of gas.
S&SE has raised prices four times since the start of 2004 but says there will be no more increases this year.
The latest increases will mean that customers of S&SE - which trades as Southern Electric, Scottish Hydro Electric and SWALEC - will have seen their gas bills rise this year by 30% and their electricity bills by 21%.
This is the biggest cumulative price rise to be imposed by any UK energy supplier so far in 2006, with Npower the other company to have pushed through two increases so far.
S&SE argued that since the start of 2004, its price rises had added up to 37% for its domestic electricity customers and 61% for gas, while the comparative wholesale price increases it has had to absorb have been 165% and 180% respectively.
Alistair Phillips-Davies, SSE's energy supply director, said: "The impact of high wholesale energy prices can only be absorbed for so long and we have delayed this price increase for as long as possible.
"In doing so, we have again imposed price rises more slowly than our competitors, an approach which has been of real help to our customers over the past two years."