Ministers are coming under increasing pressure to put the clocks forward by one hour, after campaigners claimed it would result in carbon savings equivalent to taking almost 200,000 cars off the road.

A study showed that putting the clocks forward during winter so they were one hour ahead of GMT could save almost half a million tonnes of CO2, by making evenings lighter and reducing electricity demand at peak times.

Tourism leaders in the Westcountry believe the move could bring an extra £100 million to the region, from creating an "extra" hour of daylight in the evening which could be used for leisure.

John Penrose, the tourism minister, revealed last week that the government is committed to reviewing the idea.

Businesses in Devon and Cornwall warned it would be "criminal" not to, for the benefits to tourism.

The intervention by green campaigners yesterday will step up pressure.

The 10:10 climate campaign believes setting the clocks an hour ahead of their current times all year, a situation last adopted in the UK during the Second World War, would help reduce energy use by making the evenings lighter for longer and thereby tackle climate change.

Currently, the peak time of 4.30pm to 6pm, when people are coming home from school or work, falls in hours of darkness for much of the year, so householders are switching on the lights as well as equipment ranging from kettles to TVs.

The Lighter Later campaign marked the longest day of the year yesterday by pointing out that when the sun rose at 4.43am in London, most people were asleep, but when it set at 9.20pm last night, the majority were still be awake and would be switching on lights.

A study by researchers at Cambridge University's department of engineering published in the journal Energy Policy, which will be presented at an event at Parliament today, found shifting the clocks so evenings were lighter could cut carbon.

Dr Elizabeth Garnsey, who led the research, said: "The carbon savings associated with this clock change are significant, equivalent to the carbon footprint of the production of 1,800 plastic bags for every home in Britain every year, or taking around 200,000 cars off the road."

Eugenie Harvey, director of the 10:10 campaign, which aims to get businesses, government and individuals to help cut the UK's emissions by 10 per cent, said: "In the UK we love our long summer days."