PREVIEW-Britain to unveil "route map" to low carbon future

* Britain to publish plans to cut greenhouse gas emissions

* Spotlight on nuclear, renewables, energy efficiency

By Peter Griffiths

LONDON, July 14 (Reuters) - Britain will say on Wednesday how it plans to cut greenhouse gas emissions and tackle climate change by investing in nuclear and renewable power and promoting greater energy efficiency.

Energy and Climate Change Secretary Ed Miliband will publish a "route map" for British emissions cuts of 34 percent by 2020 from 1990 levels and at least 80 percent by 2050 to avoid the "massive dangers" posed by global warming.

Britain's transition to a low carbon economy will see the country move away from imported oil and gas towards a mix of energy sources that are more sustainable, Miliband said.

"It does mean big changes in people's lives," Miliband told the BBC ahead of the publication of the government's policy document on energy.

The document will build on an agreement reached at a Group of Eight summit in Italy this month that temperature rises should be limited to 2 Celsius (3.6 Fahrenheit).

While some climate experts were lukewarm about that agreement, Miliband said it will be "very significant" in the run-up to global climate talks in Copenhagen in December.

"They have got to put offers on the table to reduce their carbon dioxide emissions which can achieve that now," he said.

"AMBITIOUS" NUCLEAR PLANS

Britain's proposals are expected to call for an enlarged nuclear programme as well as far greater reliance on renewable energy sources like wind, solar and tidal power, Miliband signalled in interviews ahead of the report's publication.

Under European Union targets Britain will have to get 15 percent of its energy from renewable sources by 2020 compared to just 1.3 percent in 2005.

"You have to be ambitious on nuclear," Miliband told the Guardian on Tuesday. "I know that is hard for some people."

The British plans will back the development of carbon capture and storage, a new technology that takes the carbon dioxide produced by burning coal and traps it underground.

They are also expected to promote energy efficiency across industry and in homes, while pushing the case for electric cars.

Miliband said the proposals would lead to higher energy prices, but said the cost of doing nothing would be greater.

Green campaigners expect the proposals to give details of feed-in tariffs, which guarantee higher prices for renewable energy producers selling energy to the national power supply.

Campaign group Friends of the Earth said it was important that Britain meets its emissions targets through cuts at home rather than relying on buying overseas carbon offsets.

"There has been far too much hot air on climate change -- now we need tough and urgent action," Executive Director Andy Atkins said in a statement. (Editing by Robin Pomeroy)