British Gas doubled profits in the first half of the year, as its parent firm announced thousands of job losses.

Centrica said 6,000 posts would be cut across the group, around 10% of its workforce, although 2,000 new jobs will be created so the net loss will be 4,000.

Oil giant Royal Dutch Shell, meanwhile, has said it plans to cut 6,500 jobs this year.

The Centrica cuts follow a review which is aimed at delivering savings of £750 million over five years.

British Gas profits were £528 million for the first half of the year, more than it made in the whole of 2014, even though it cut prices by 5% earlier this year.

Not all the job cuts will be in the UK, while around half are expected to be through redundancies.

British Gas' operating profit was up by 44%, according to interim first half results from the group, which was larger than expected.

The company said this was because of a colder year compared to 2014, with consumption up by 11%.

Centrica's group adjusted operating profits fell 3% to £1 billion.

Which? executive director, Richard Lloyd said: 'While it's good to see the new commitment from Centrica to focus on serving customers, with British Gas profits high and wholesale prices low, customers will no doubt wonder why cuts to their bills haven't gone further, and haven't included electricity.

'The Competition and Markets Authority (CMA) has confirmed that household bills should be lower if the energy market was truly competitive. Following the CMA's blistering assessment of this sector, we expect big suppliers to pass on falling costs to their customers quickly and fairly.'

Ann Robinson, director of consumer policy at uSwitch.com, said: 'The news that British Gas is predicting a surge in profits will be a hard pill to swallow for its customers, especially as so many went cold last winter to cope with sky-high bills.'

Royal Dutch Shell, meanwhile, said it was taking action amid a slump in oil prices and that it was 'planning for a prolonged downturn' as it slashed costs for 2015 by 10% or £2.6 billion.

Further cost-cutting is expected in 2016.

Chief executive Ben van Beurden said: 'We have to be resilient in a world where oil prices remain low for some time, whilst keeping an eye on recovery.'