Energy prices are up across the board

It said it would raise prices by between 8.9% and 12% for electricity and 13.6% for gas customers.

The company blamed higher wholesale gas and electricity prices for the rise.

Power watchdog Energywatch said the timing of the rise was poor, coming just after Christmas, which was an expensive time of year for consumers.

The last time that SSE put up its prices - in February - it promised it wouldn't increase prices again until at least 2006.

The firm said that it had no choice but to increase prices when the time constraint expired.

"The pressure of high wholesale prices cannot... be withstood indefinitely and we have come to the point where these price rises are unavoidable," said Alistair Phillips-Davies, SSE's energy supply director.

Oil price link

In recent months, Powergen, EDT Energy and Scottish Gas all increased prices.

High oil prices has been the main reason for the higher charges.

This has driven up the price of gas imported from the continent, where the wholesale price of gas is linked to the price of oil.

In turn, this has made it much more expensive to generate electricity in the UK's gas-fired power stations.