Scottish & Southern Energy, which has 8.8 million UK customers, said the full impact of soaring oil costs on electricity and gas prices "has still to be felt".

Chief executive Ian Marchant said: "We are continuing to resist the pressure to put up prices for domestic customers, but doing so is becoming more difficult by the day."

SSE's warning is the latest sign that households coping with soaring food prices should also brace themselves for higher energy bills.

The firm told investors that profits in the six months to September 30 would be "substantially lower" than the previous years but said the majority of its profits would be made between October and March - a clear signal that price hikes are on the way.

In May the group posted a 13.9 per cent rise in underlying pre-tax profits to £1.23 billion for the year to March, but added today that it expected a "modest increase" in profits in the current year.

A surge in wholesale gas costs has already prompted a raft of higher tariffs from the "big six" UK energy firms in January - prompting a probe by energy regulator Ofgem - although SSE held off until March to lift its own prices.

The hikes have added to the problems faced by Bank of England interest rate-setters as inflation rises above target.

SSE, whose businesses include Southern Electric, Scottish Hydro Electric and Swalec, said it had made progress with major projects such as electricity generation schemes at Glendoe near Loch Ness and Marchwood, Southampton.

The company is also boosting its portfolio of energy from renewable sources after forming a joint venture with Forth Ports to develop sustainable energy schemes, as well as new wind farms in Portugal, Italy and Clyde in Southern Scotland.

Last year, Scottish & Southern revealed that its coal-fired Ferrybridge Power station in West Yorkshire could remain operating for several decades.