Holidaymakers booking through the Co-operative Group's chain of high-street travel agents will be prompted to counter the environmental effects of their journeys, under a new carbon-offsetting scheme launched today.

In a first for high-street travel agencies, the voluntary scheme will allow customers to pay on the spot to offset either all of the carbon dioxide produced by their flight, or a 20% portion of it inline with government emission reduction targets. Consumers will be offered eight price bands reflecting the distance travelled, ranging from £3 for a short-haul flight to France or mainland Spain to £50 for a holiday to Australia or New Zealand.

Aviation is the fastest growing source of carbon dioxide emissions. Since 1970, the number of people using British airports has risen more than six-fold, from 31 million a year to 215 million a year in 2004. The carbon offsetting will be implemented by Climate Care via funding for carbon-reducing projects such as energy-efficient stoves in India or reforestation in Africa, which will, over a period of time, counter a similar amount of carbon dioxide as a particular flight.

The initiative - the first to be made available on the high street rather than online - will be trialled in five Travelcare agencies, before being rolled out to all 340 branches nationwide by the end of the year. Customers who opt in to the scheme will receive a certificate and luggage tags declaring that their travel has been carbon offset.

It is the third offsetting scheme to be introduced by the Co-operative Group, which already contributes to Climate Care on behalf of its mortgage and car insurance customers. Last year, the group's contribution on behalf of mortgage customers amounted to £250,000, or a tonne of carbon dioxide per customer.

As regular foreign holidays were "not an essential", it was appropriate that customers, rather than the company, be asked to pay for the flight-related offsets, according to Paul Monaghan, the Cooperative Group's head of ethics and sustainability.

"It is very hard to work out the typical mileage for a typical holiday," he said, adding that the price bands would simplify the process for customers.

"Over next 10 years, carbon offsetting will be a vital way to engage the public and the government to tackle climate change. This is a genuine transferral of large sums of money from the first world to the third world for investment in renewable technologies."