Npower is to close offices and outsource work to India in a move that will see 1,460 UK staff lose their jobs at the energy supplier.
The company confirmed it will close its office in Stoke on Trent and one of three offices in Oldbury in the West Midlands as back office customer service functions are moved to India over the next eight months.
There will also be redundancies at its Rainton Bridge base in Sunderland, and in Leeds, while a further 540 jobs will be transferred to British firm Capita.
The npower chief executive, Paul Massara, said that while the changes would be "incredibly hard for some of our employees", they were necessary "to deliver the levels of service our customers deserve".
He added: "We would have the flexibility to keep call waiting times down during busy periods, and continue to keep costs down so we can keep bills down. All calls would still be answered in the UK."
The announcement is expected to intensify public anger around the activities of the Big Six power companies and raise the political heat in Westminster where energy has risen to the top of the agenda.
Trade unions accused npower of serving up a "Christmas nightmare" by announcing plans to move back-office jobs to India using Tata Consultancy Services and transfer hundreds of front-line call centre jobs to Capita.
Npower staff at other locations will also be affected by the plans, which include the closure of its Thornaby office in the north-east, where staff will keep their jobs if they are prepared to relocate to the company's Rainton office about 30 miles away.
Several teams currently based in Peterlee will also be required to move to Rainton if they want to keep their jobs.
Union leaders warned the moves would backfire and further tarnish the reputation of npower, which came bottom for customer service in a recent survey and which told a parliamentary committee earlier this year that it had paid almost no corporation tax for three years.
Npower, the energy supplier of Germany's RWE, hit gas and electricity customers with a 10.4% rise in fuel bills earlier this month and its central London offices were the target of fuel poverty demonstrations earlier this week.
The company, which employs 11,000 in the UK, informed staff of the changes on Thursday morning, after details had already appeared in the press.
Npower and the other big six firms such as SSE and Centrica insist that they are having to raise domestic bills and trim their costs in a bid to counter the impact of rising wholesale prices and green levies for home insulation.
Npower's parent RWE said earlier this month that 6,750 jobs would need to be cut across Europe as it tries to reduce a debt mountain of over £28bn, partly caused by the Berlin government's decision to phase out nuclear power stations.
In Britain RWE shelved plans for a £4bn wind farm in the Bristol Channel this week, a week after it sold off part of its gas and electricity supply business. It has also put up for sale its DEA business which operates oil and gas fields in the UK North Sea and also shelved plans to construct new nuclear plants in Britain.
But Matthew Lay, national officer with the Unison union, said npower had consistently let its customers and staff down by not investing enough in the workforce, technology or in the latest customer service techniques.
"This has led to a huge number of complaints which the company seems to think they can deal with by shifting the responsibility to somewhere else, including to India.
"If the company goes ahead with this disastrous plan, it will backfire badly, damaging their already tarnished reputation for customer service.
"At a time when unemployment is high, what commitment does it show to the UK by shipping these much-needed jobs abroad? And what does this say about their commitment to staff when npower have kept them on tenterhooks, waiting for the axe to fall, for weeks?"
Colin Smith, the GMB union's northern region senior organiser, said his union would vigorously campaign against the offshoring of jobs to India because it had absolutely "nothing to do with customer service and everything to do with cost".
"This is about the cost of living, bad management and naked greed. At this time of the year when the Christmas lights are being turned on for most people, npower workers, their families and communities have no yuletide greetings," he said.
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