Energy chiefs will be asked to defend expected future rises in fuel bills when they appear before MPs on Tuesday.
Big increases in gas and electricity bills are likely this year, leading energy suppliers have confirmed.
Bosses of the big six energy firms are answering questions about prices from MPs on the parliamentary business and enterprise select committee.
Sam Laidlaw, the chief executive of Centrica, which trades as British Gas, said it was "clear that gas prices are going to have to move up".
He acknowledged that predictions of 40% price rises could be accurate.
Rupert Steele, director of regulation at Scottish Power, said: "The whole industry figures will have to rise significantly."
Their comments came as MPs on the committee started asking them to defend the big increases in gas and electricity prices facing households and businesses in the UK.
Mr Laidlaw said: "Our absolute price levels are currently the lowest in Europe.
"As we import more gas from continental Europe, we are having to pay higher prices," he explained.
Both Scottish Power and Scottish and Southern Energy pointed out that they had to buy all their gas on the international markets, as they do not produce any gas or oil in their own businesses.
Mr Laidlaw said it was not fair for him and his rivals to be described as "fat cats".
"The average profit margin is 3.5% in the industry," he said.
Price pressures
Domestic suppliers are under pressure to explain pricing intentions after the BBC learnt that household energy bills could rise by up to 40% this winter.
Domestic suppliers are under pressure to explain pricing intentions after the BBC learnt that household energy bills could rise by up to 40% this winter.
Centrica is among the companies giving evidence to MPs
Industry sources have suggested households could pay £400 more a year on average for gas and electricity.
Industry sources have suggested households could pay £400 more a year on average for gas and electricity.
Suppliers have said they are reacting to the sharp jump in wholesale gas costs, triggered by rising oil prices.
"It is easy to see how you get to the BBC's figures", said Mr Steele for Scottish Energy.
Executive parade
The wholesale gas price is closely linked to the price of oil, which itself hit a record high of just under $140 a barrel this month.
The wholesale gas price is closely linked to the price of oil, which itself hit a record high of just under $140 a barrel this month.
Industry research has suggested wholesale gas prices have risen by more than 70% in 2008. Last month, Centrica - which owns the UK's biggest energy provider, British Gas - signalled that gas prices for customers could increase again later this year.
Industry research has suggested wholesale gas prices have risen by more than 70% in 2008.
Centrica's chief executive Sam Laidlaw is among senior industry figures due to appear before the Commons Business and Enterprise Select Committee on Tuesday.
Last month, Centrica - which owns the UK's biggest energy provider, British Gas - signalled that gas prices for customers could increase again later this year.
Centrica will be among the companies giving evidence to MPs
MPs are also pressing energy chiefs on the extra help being given to low-income and disadvantaged households to help them with the impact of rising bills.
MPs, who are looking into competition in the retail energy market, want to know what suppliers expect to happen to fuel bills over the winter
Watchdog Ofgem, which is conducting its own inquiry into the market, outlined plans last month to share data on people on low incomes with energy companies to help people pay their fuel bills.
They will also press energy chiefs on the extra help being given to low-income and disadvantaged households to help them with the impact of rising bills.
Watchdog Ofgem, which is conducting its own probe into the market, outlined plans last month to share data on people on low incomes with energy companies to help people pay their fuel bills.
The proposals, which must be approved by Parliament, are designed to ensure that financial assistance for fuel payments can be better targeted at the elderly and vulnerable.
The proposals, which must be approved by Parliament, are designed to ensure that financial assistance for fuel payments can be better targeted at the elderly and vulnerable.
Fuel poverty
Fuel poverty
The government estimates that 2.5 million households are in fuel poverty - defined as when more than 10% of household income is spent on fuel bills - but watchdog Energywatch says the figure is more than four million.
The government estimates that 2.5 million households are in fuel poverty - defined as when more than 10% of household income is spent on fuel bills - but watchdog Energywatch says the figure is more than four million.
A 40% rise in average fuel bills would be far higher than expected and would put more pressure on homeowners already struggling with higher food and fuel costs.
A 40% rise in average fuel bills would be far higher than expected and would put more pressure on homeowners already struggling with higher food and fuel costs.
However, some analysts believe the increases will be closer to 25%.
However, some analysts believe the increases will be closer to 25%.
It is thought that any price announcements are most likely to come in August, when energy bills are not at the forefront of people's minds.
It is thought that any price announcements are most likely to come in August, when energy bills are not at the forefront of people's minds.
But there is a great reluctance in the industry to be the first to reveal a big rise, so the rises may be unveiled in stages.
But there is a great reluctance in the industry to be the first to reveal a big rise, so the rises may be unveiled in stages.
The chief executives of Scottish & Southern Energy, NPower, EDF Energy and E.ON UK will also attend the meeting while Scottish Power will also be represented.
The chief executives of Centrica, Scottish & Southern Energy, NPower, EDF Energy and E.ON UK are attending the meeting, while Scottish Power is also represented.
Are you struggling to pay your gas and electricity bills? Are you worried about future rises in in your household energy bills? Send us your comments using the form below:
Are you struggling to pay your gas and electricity bills? Are you worried about future rises in your household energy bills? Send us your comments using the form below:
