Centrica is unable to give customers assurance that wholesale prices for gas will remain low until the end of 2007 after falling rates allowed its subsidiary, British Gas, to reduce residential bills twice so far this year.

In a statement released before its Annual General Meeting today, Centrica said that while the outlook for its business was encouraging, "significant uncertainty remains over wholesale gas and power prices for the balance of the year and over demand levels due to unusual weather patterns".

However, shares in the company rose to 391.25p from 385p in early trading as the company said that if wholesale prices remain in line with forward market prices and temperatures are seasonally normal, group operating profit for the year to December 31, 2007, will be above market estimates.

Gas production in Centrica's wholesale, or "upstream" business, fell by 48 per cent compared with the first five months of last year, although electricity generation grew by 133 per cent.

While upstream profits - from wholesaling energy to other suppliers - have fallen, downstream income, generated through the sale of gas and electricity to homes and businesses, has been bolstered and after the first of two price cuts, 900,000 customers decided to join British Gas.

However, British Gas emerged as the worst energy provider in the UK for the second year in a row as part of a survey by uSwitch, the online billing comparison company.

The company failed in a number of areas, including overall customer satisfaction, providing the best deal and value for money. Although, British Gas was commended for its meter reading services while npower emerged as the worst provider of customer services.

Centrica said today that so far this year it has added 800 customer service staff to its 10,000 UK workforce and is investing £430 million in a new billing system.

In response to uSwitch's findings, Centrica said: "This survey is misleading as it was carried out before our second price cut. We have the cheapest dual fuel tariff on the market. Not only are we the cheapest, we are also the greenest — with the lowest emissions of all major UK energy suppliers.

"Earlier this week the Reader's Digest survey voted British Gas as the most trusted brand out of the energy suppliers. We are investing to improve customer service and this is having results — even uSwitch’s flawed survey shows British Gas is not bottom for customer service."

Times Recommends

• Gazprom brands Ukraine 'a barbarian' in gas row
• Services sector raises fears over UK jobless
• Retailers surge as profits survive sales plunge