For how long can we take unrestricted business travel for granted? Calls for British businesses to reduce their 'environmental footprint' will be bolstered by research which found that work-related air travel last year contributed 5.4 million tonnes of CO2 emissions. Last year UK employees clocked up 26.5 billion air miles - enough for 275 return trips to Mars - travelling abroad.

Worryingly, British workers appear unconcerned about the environmental consequences of all those flights. The same research, conducted by YouGov on behalf of the Portman Travel Group, found that only 7 per cent of UK employees think climate change is an important issue for bosses. But while nearly 60 per cent of employees think that their bosses should donate more of their profits to protect the environment, 77 per cent would not themselves be prepared to make a personal contribution.

So what can businesses do about it? Fly less often is the obvious response, but it is unlikely that enough people will do this to make a major difference. Others advocate the use of video conferencing to reduce the need for plane journeys. But an idea gathering force is that of companies 'spending' their way out of the environmental problems associated with aviation. More people are contributing to schemes allowing them to offset their share of the carbon emissions caused by flying.

One such scheme is run by The CarbonNeutral Company, which specialises in climate change issues. It allows businesses and individuals to offset their environmental footprints by investing in a wide range of initiatives - from windfarms and forestry schemes to solar lighting in rural India - that soak up, reduce, or avoid carbon emissions. Its clients include Honda, Avis Europe and Berkeley Homes.

The CarbonNeutral Company calculates that it would cost £65m to offset those CO2 emissions caused by employees flying abroad in 2005. For example, the cost of offsetting emissions on individual return fares would be £1.50-£3 for a London-Frankfurt flight, £10-£17 for London-LA and £27-£36 for London-Sydney. The price ranges reflect the varying costs of different projects that can be invested in.

According to Jonathan Shopley, chief executive of The CarbonNeutral Company: 'The carbon dioxide emissions generated by business flights can be one of a company's largest impacts on the climate. However, travel emissions can also be an area where great opportunities for positive action are available.'

Portman Travel has launched 'Portman Forest' in partnership with The CarbonNeutral Company. The scheme enables and encourages customers to offset their CO2 emissions generated by domestic and international travel by supporting renewable energy, energy efficiency and sustainable forestry projects.

'Portman Forest is an easy and practical way for businesses to demonstrate that they take corporate social responsibility seriously,' says Graham Flack, managing director of Portman Travel. 'Since 1983, the number of overseas visits by UK residents has increased more than threefold to 66 million journeys a year. The rise in international travel poses a threat to the environment. It is important that responsible organisations within our industry look at ways of reducing greenhouse gases caused by their operations. Our customers travelled nearly 900 million kilometres [560 million miles] by air last year. This gives Portman a unique opportunity to help them become "ecosmart" by reducing their environmental footprint.'

However, green campaign group Friends of the Earth is not convinced this is the full solution. It believes the government needs to reverse its policies allowing aviation growth.

Gordon Brown was criticised for his failure to raise air passenger duty in this year's Budget to help achieve the government's environmental targets. An influential group of MPs described this as 'incoherent' and 'unconvincing'. The Labour-dominated Commons Treasury select committee urged the government 'to re-examine whether it is making the fullest possible use of taxation instruments as a mechanism to achieve [its] environmental targets'.

The airline industry is gearing itself to defend its environmental credentials. At a conference last month, Willie Walsh, new chief executive of British Airways, said: 'While it is crucial that aviation takes action on emissions, the notion that flying is a selfish, antisocial activity that singlehandedly threatens planetary catastrophe bears no relation to the evidence.'

Executives from low-cost airlines Flybe and Easyjet have joined Walsh in mounting strongly worded attacks on environmentalists, who they believe peddle 'myths'. Easyjet says its business model reduces its impact on the environment. '[Our] stated aim is to operate a fleet of young aircraft,' the company says. 'These have lower noise emissions and use less fuel than earlier models. Easyjet is implementing a fleet replacement plan that will result in a fleet entirely composed of Boeing 737 New Generation and Airbus A320 family aircraft, which will have all been purchased from new.' Ryanair makes a similar argument, and is among the most aggressive in defending itself against further taxation.

BA is in a minority among its peers as it is happy to trade its emissions - buying credits from other less polluting companies. It already voluntarily participates in the UK Emissions Trading Scheme. In addition, the airline is trying to achieve a 30 per cent improvement in its aircraft fuel efficiency between 1990 and 2010 and a 2 per cent a year reduction in energy consumption in its buildings.

high-flying engines of damage

= Most scientists believe that aviation is a significant contributor to global warming. Aircraft engines produce large amounts of greenhouse gases, CO2 in particular. The build-up of these gases in the atmosphere means that more of the sun's warmth is trapped. The concentration of CO2 has increased by about 25 per cent since 1950. = Some scientists say that emissions at high altitude seem to do more damage than those at ground level. Aircraft account for about 4 per cent of the world's CO2 production, but emissions from aviation are increasing, partly because the number of low-cost flights has grown. In Europe these have more than doubled in five years. And forecasts suggest that by 2030 aviation could represent up to a quarter of the UK's total contribution to global warming. = According to the University of East Anglia, the average person in Britain is responsible for the environmentally-damaging production of about nine tonnes of CO2 each year. But a return flight to Cape Town, for example, would add about 2.15 tonnes to this. Anyone who chooses to fly frequently could end up doubling the amount of CO2 production for which he or she is responsible. = The number of work-related flights taken by British businesspeople is predicted to increase from today's average of 7.6 flights a year to 8.5 per year in 2015, according to a recent survey by Barclaycard Business. And people will soon be travelling longer distances: the number taking seven or more long-haul flights a year is predicted to increase from 6 per cent in 1997 to 14 per cent in 2015.