Millions of households are facing further misery after Powergen raised energy bills by as much as 18.4 per cent.

It became the latest major supplier to impose massive increases in household bills when it said gas prices will go up by 18.4 per cent and electricity by 9.7 per cent on Monday.

The German-owned supplier blamed an 87 per cent increase in the cost of buying wholesale energy to sell on to its customers in the UK since the beginning of last year.

It came just two days after Powergen owner EON said profits at its UK arm plunged 26 per cent because of the soaring cost of wholesale gas.

In March, Powergen -which has 8.5 million customer accounts in the UK -lifted the price of gas by 24.4 per cent and electricity by 18.4 per cent.

But despite falling profits at Powergen, group profits for Dusseldorf-based EON rose 13 per cent to 4.84 billion euros (pounds 3.26 billion) in the first half of the year.

Yesterday's move means that every major supplier in the UK has now imposed two rounds of price increases this year, including British Gas whose customers face a 12.4 per cent rise in gas bills and 9.4 per cent in electricity bills on September 4.

The higher prices come hot on the heals of similar moves by EDF Energy, Scottish Power, npower and Scottish & Southern Energy.

Consumer group Energy-watch said it was "another blow" to households already struggling with debts and higher interest rates.

Energywatch said an average Powergen gas bill was now pounds 644 a year - up 107.5 per cent since 2003 - while the average electricity bill was pounds 333 - up 62.1 per cent.