LONDON - Britons could soon be making money out of a greener lifestyle under a government proposal for personal carbon emissions allowances.

A government study will focus on personal carbon caps which, if adopted, could allow the public to cash in if they cut down on their emissions of carbon dioxide, which contributes to global warming.

Those who produce less carbon under their personal cap could earn credits, which might be used like points on a loyalty card or sold on to those who pollute more.

The plan will be unveiled by Environment Secretary David Miliband later today.

"Imagine a country where carbon becomes a new currency," Milliband will tell the Audit Commission's annual lecture. "We carry bank cards that store both pounds and carbon points. When we buy electricity, gas and fuel, we use our carbon points, as well as pounds."

Under the proposed scheme, carbon allowances would cover energy use through electricity, gas, petrol and air travel. Such emissions make up 44 per cent of total UK emissions.

"People on low incomes are likely to benefit as they will be able to sell their excess allowances," Milliband will say. "People on higher incomes tend to have higher carbon emissions due to higher car ownership and usage, air travel and tourism, and larger homes."

Personal carbon allowances are one of several options Britain is looking at to help the public get involved in tackling climate change.

Other ideas include carbon loyalty cards, league tables, the use of carbon offsets at point of purchase for certain sectors, product carbon labelling and carbon calculators.