New nuclear power stations may not be the best option for keeping Britain’s lights on and meeting the country’s carbon targets, the Liberal Democrats have said.

The party said there were legitimate concerns over nuclear’s cost and the risks it would not be delivered on time, just days after windfarms secured state support far more cheaply than the Hinkley Point C atomic power station.

However, the party, which voted in support of nuclear four years ago after decades of opposition, said the technology should still be considered an option in the UK’s future energy mix.

“Nuclear power should be kept open as an option – but there is a risk that it may not be able to keep the lights on and that it may not be the lowest-cost option,” said the Lib Dems in a new report, authored by the former coalition minister Lynne Featherstone.

Vince Cable, the party’s leader, said this week that the breakthrough low subsidy prices for offshore windfarms should prompt a “radical reappraisal” of how Britain is powered.

If the Lib Dems were to go so far as opposing atomic power again, it would mark a break in the pro-nuclear cross-party consensus of the three main parties.

Senior Lib Dems believe the party has an opportunity to seize the momentum on environmental issues, with Labour constrained on issues such as nuclear power because of its close association with trade unions.

Ed Davey, the Lib Dem MP and former energy minister who was pivotal in the party’s support for nuclear, said of the report: “It’s not about taking nuclear off the table. It’s responding to the evidence of the last two years.

“It’s a recalibration off the back of the fact nuclear is not proving to be a practical, affordable technology. It’s not saying never [to nuclear], but the costs are coming down fast with renewables.”

The report also backed an acceleration of renewable energy, carbon capture and storage (CCS) and greater flexibility of the energy system through storage and interconnectors with other countries.

The party accused the Conservatives of “unravelling” progress on climate change made by the Lib Dems during the coalition government years.

“What worries me about the Tories is they have taken CCS off table, they’re not pushing forward with renewables,” said Davey.

The report concludes that the UK is on course to miss its contribution towards the Paris climate agreement aspirational target of keeping global temperature rises below 1.5C.

To get back on track, the Lib Dems are calling for the Climate Change Act’s target of an 80% cut in carbon emissions by 2050 to be brought forward by five to 10 years.

Last year the government’s climate advisers warned that the UK lacked policies to meet half of the carbon reductions required by 2030. Ministers have produced a blueprint on how to close the gap, the Clean Growth Plan, which could be published as soon as next week.

Before the party’s annual conference in Bournemouth this weekend, Cable said the world would “soon reach a tipping point beyond which catastrophic global warming will become irreversible” and Britain had a responsibility to set an example.

“Instead, these past two years the Conservatives have done their best to trash our green industries and undo the progress made during the coalition years,” he said.

“This report shows that becoming carbon-free by 2050 will be crucial if we are to meet the Paris agreement’s ambitious target of limiting temperature rises to 1.5 degrees. Furthermore, it sets out how this ambition can be delivered.”

The party will also hope to burnish its environmental credentials in the coming months with the debate over Heathrow expansion, which it opposes. The majority of Labour MPs are in favour of expansion, as is the Unite trade union, although the Labour leader, Jeremy Corbyn, and shadow chancellor, John McDonnell, are against further expansion.