Britain's ageing nuclear reactors, which were due to close in the next decade, are set to be kept open under a plan approved by the industry's regulator.

In a move that could have far-reaching implications for the government's energy policy, the Office for Nuclear Regulation has told the Guardian it is working with the country's dominant nuclear operator, the French-owned company EDF, to extend the life of its eight nuclear power stations in the UK, and that it is "content for the plants to continue to operate", as long as they pass regular safety tests.

The two organisations are also discussing other improvements to EDF's plants, including monitoring systems and dealing with the reactors' ageing.

Just a few weeks ago ministers were still referring to the need to "keep the lights on" in Britain when a number of existing nuclear and coal power stations closed over the next few years, by building new nuclear and gas power and subsidising renewable energy technologies and carbon capture and storage.

The plans have emerged as the government prepares to publish its energy white paper , setting out plans to introduce a guaranteed minimum price for the power produced by low-carbon generators to encourage an estimated £110bn investment in nuclear and renewable energy, and carbon capture and storage equipment that traps emissions from new gas stations. EDF said it has yet to make a formal decision, but the first power stations which could be submitted for another periodic safety review (PSR) to remain open beyond their planned closure were Hinkley B in Somerset and Hunterston B in Ayrshire, both of which were due to shut down in approximately 2016.

The company has said it wants to extend the life of seven of its plants for an average of seven years, a figure it has already raised from five years and which could increase again if EDF decided it was commercially viable to keep them open longer. Its other plant, Sizewell B in Suffolk, is expected to remain open until 2035.

Plans to keep the nuclear plants open will encourage critics of the government's energy policy, which calls for expensive new nuclear reactors to meet short- to medium-term demand while renewable energy such as wind, solar and tidal power are improved so they can be deployed on a mass scale.

The government is also betting on carbon capture and storage technology to enable gas powered stations to keep burning fossil fuels without breaching tough limits on future carbon emissions.

Tom Burke, a former head of Friends of the Earth, lobbyist and visiting professor at Imperial and University Colleges, London, said EDF's decision had been "always on the cards" since the government put in a carbon floor price.

The floor price gives low-carbon energy producers like nuclear, as well as renewable companies, an advantage by making fossil fuel burners who run coal and gas plants pay a minimum amount for each unit of carbon produced from their power stations.

The policy, announced in last year's budget, begins in April 2013 at £15.70 per tonne of carbon – more than double the current market price. That rises to £30 per tonne at the end of the decade. At £15.70 the UK power industry would have had to pay more than £3bn for the carbon price alone, based on a 2007 estimate of its total emissions.

"Effectively the carbon price will pay the costs of the life extension, and then some," said Burke.

"There never was a plausible energy security argument for building new nuclear: they thought it was a cheap way of getting a transformation to low carbon. [Life extension] buys us time for renewables and carbon."

The plans to keep the plants open follow a difficult few months for the government's nuclear programme with one of the two leading consortiums bidding to build new reactors pulling out, citing the political fallout from the Fukushima nuclear leak in Japan after the tsunami in that country, and reports that one of the major credit rating agencies could downgrade the rating – and so increase the cost of debt – for EDF and its new-build partner Centrica, if they went ahead with plans to build four new reactors.

EDF said: "Extending the lives of our nuclear power stations makes absolute sense in terms of filling a short-term energy need while the country rightly continues towards aggressive decarbonisation targets."

However the company said it was still fully committed to building new reactors, dismissing suggestions that the life extensions would undermine the need for new capacity.

"Life extension helps with the very short-term risk but doesn't change the need or urgency of the new nuclear programme in the longer term," said a company spokesman.

"The fundamental need for new capacity remains: the inability of old coal to meet tighter emissions limits being the foremost factor."

EDF did not need specific permission from the Office for Nuclear Regulation to submit the plants for the next 10-yearly periodic safety review, but said it had raised its intentions with the regulator because it liked to work with the regulator on a "no surprises" basis.

Robert Gross, a leading energy expert at Imperial College, London, said he was surprised the life extensions were not expected to cause more safety issues, but said that the decision could buy time for the energy industry, which was struggling with demands to build new gas, nuclear and renewable energy in a short period of time, including problems raising finance. "Another advantage would be we'd have more clarity on how successful we were being with renewables," said Gross.

The Department of Energy and Climate Change said on Monday: "Extending the lifetime of old nuclear plants will only give us a few more years of power. We will be shifting a problem to another day. New nuclear is where the future lies for long-term energy security. This is why it is so important we begin the transition on market reform today."