EDF Energy is increasing its electricity prices by 17 per cent and its gas prices by 22 per cent from today.
The French-owned firm, which has five million customers in London, the south-east and the East Anglia, blamed the price hike on rises in wholesale energy prices since its last price rise in January.
A typical customer on a dual fuel tariff will pay £3.97 a week more for their energy.
The firm claims coal prices have risen 70 per cent, gas prices have risen 93 per cent and electricity prices are up 47 per cent.
Eva Eisenschimmel at EDF Energy, said: Record world oil prices have continued to drive up wholesale gas prices this has impacted hugely on the cost of supplying energy to our customers.
"We have been absorbing some of these costs in recent months, but we now have to pass on some of the resulting rise in wholesale costs to our customers."
EDF is reaffirmed its moves to aid consumers facing fuel poverty.
Some 100,000 of the firms most in need customers are set to benefit from a 15 per cent discount following major expansion of the firm's social tariff.
Yesterday Scottish & Southern Energy (SSE) hinted at further price rises for customers, following a report last week from British Gas-owner Centrica that average gas bills alone could rise to over £1,000.