If there's one predictable thing about the debate between environmentalists and those focused on business growth, it's that the arguments tend toward the extreme.

Take the current brouhaha over the Heathrow Airport expansion, for example. To environmentalists, the airport exhibits all the characteristics of a cancer. It grows where it shouldn't, it expands aggressively, and consumes the surrounding environment. For supporters, including the Department of Transport, it is a vital organ supporting the UK economy, and should be nurtured and strengthened.

It has certainly grown aggressively enough. What was originally a tent and a grass strip in the 1920s and 30s has turned into one of the world's busiest airports, employing 68,000 people and processing a thousand times as many passengers each year. But for the Department of Transport, its 470,000 flights a year aren't enough. A proposed third runway and a sixth terminal (in addition to the fifth one, due to open in March), would take that figure to 700,000 flights per year. Business advocates argue this expansion is necessary to support economic growth and create jobs; environmentalists are left fuming.

But what if your company straddles both communities? Companies with an ethical focus may feel themselves torn. When this topic comes up in conversation, what position should green businesses take?

Now is the time to think it over; after announcing the expansion plans in a consultation document in November, the government invited comments. Concerned parties have until 27 February to register their opinions.

The Confederation of British Industry doesn't maintain a specific position on the Heathrow expansion, according to head of infrastructure Karen Dee.

"Our basic position is that aviation is pretty important for the economy, and it's a successful industry," she points out, citing figures from a report by Oxford Economic Forecasting. According to that report, the aviation industry creates around 186,000 jobs directly in the UK (contributing around $11.4bn to UK GDP in 2004).

Moreover, it created more than 300,000 more jobs indirectly, in companies that rely on aviation for their business, and many experts maintain that London's position as one of the world's financial capitals and the south east's role as the country's economic engine room owe a great deal to the health of Heathrow.

That economic argument doesn't impress John Stewart, chairman of HACAN Clearskies, a pressure group dedicated to curtailing growth at Heathrow.

"We would argue that the environmental and social downsides of expansion are unacceptably high," he says, categorising them into three main areas: climate change, housing and noise.

The climate change issue has the broadest scope, of course, because it affects everyone, rather than merely those west London residents closest to Heathrow. The aviation industry has argued that the third runway will deliver some carbon savings as the increase in capacity will mean far fewer planes will have to circle while waiting for a landing slot. BA has claimed that a third runway could save 330,000 tonnes of CO2 a year. But with the third runway also enabling 220,000 extra flights a year, official government figures estimate the net carbon impact will be an increase in emissions of 2.6m tonnes a year.

The economic case for Heathrow may be solid and any business traveller who has wasted hours battling through the scrum at the airport's crowded terminal will find it hard not to want to support calls for expansion. But equally there is little doubt that the growing numbers of businesses that have committed themselves to cutting their own carbon emissions could leave themselves open to charges of hypocrisy by supporting such a carbon intensive project, particularly when alternatives such as high-speed rail links to the continent and video conferencing technologies are now available.

For Stewart, noise pollution is also a huge issue. "The government argues implausibly that we can get this huge increase in the number of planes using Heathrow and noise levels will be lower than they are now," he says.

He argues that the government's latest report into the proposed Heathrow expansion is directly at odds with its previous commitments in its 2003 aviation white paper, The Future of Air Transport. That document assumed that the community annoyance threshold was 57 decibels (dbA). The community annoyance threshold is the point at which the collective tutting over average airplane noise in an airport's neighbourhood becomes uncomfortably audible in parliament. Section 11.53 of the 2003 white paper says "any further development could only be considered on the basis that it resulted in no net increase in the total area of the 57dBA noise contour compared with summer 2002, a contour area of 127sq km".

However, an independent assessment published in November found that the idea of a single threshold is invalid. The government spent untold amounts of cash on the Attitudes to Noise from Aviation Sources in England (ANASE) report to reveal that the relationship is more linear. Instead of living in a state of sanguine bliss until plane noise reaches 57dbA and then suddenly hopping up and down with rage, the report's shocking conclusion was that people simply get more annoyed the louder the planes get. Other factors such as household income and changing attitudes to society may come into it, too, the report found.

Stewart's argument is that this makes the idea of 'community annoyance' a moveable feast, effectively meaning Heathrow expansion will break the government's 2003 commitment not to increase the number of people that it ticks off with airplane noise.

Cynics might wonder why the government had to spend untold amounts of cash on a report to state something that seems deafeningly obvious. Politicians known that it's because you need a set of figures to point to when opposing parties criticise your idea. However, the government will not be pointing to the ANASE figures. Its consultation paper on the Heathrow expansion, published three weeks after the ANASE report, accepted the proposal that a step-change in annoyance did not exist, but dismissed the study as unreliable, and stuck to the 2003 white paper as the best bet.

On the housing side, Stewart worries that the number of homes affected by the expansion will be hundreds more than the government's estimate of 700. Those left yards from the airport will be effectively uninhabitable, he argues.

But what can businesses do given the importance of corporate travel?

Offsetting demand with other modes of transport is a key option, Stewart says, who claims 100,000 of Heathrow's annual flights are to 12 destinations for which there are viable rail alternatives.

"We argue that the government should be looking at limiting the number of slots for these short-haul flights when there's a good rail alternative," he says, adding that Heathrow sends tens of flights to Paris each day. "Then you can free up space to increase significantly the number of long-haul flights coming into Heathrow. It can therefore be a business-friendly airport without expanding."

"We welcome the fast links that we now have, but it doesn't support links to everywhere," counters the CBI's Dee. There is no high-speed rail link to the north of England, for example, and train links to European locations beyond Paris and Brussels still take significantly longer than flights.

She argues that the solution to aviation's emission problem lies in including it in emissions trading schemes rather than intervening directly to limit expansion. Such a move would put a price on carbon emissions for airlines and provide them with a financial incentive to invest in greener aircraft and business process, while the knock-on impact on ticket prices would further encourage travellers to look at alternative means of transport. It is a potential backed by both the UK government and the EU, which plans to pull the aviation sector into its emissions trading scheme from 2011, despite opposition from many within the aviation industry.

That will provide some succour for businesses suffering a crisis of conscience over whether to support Heathrow's expansion, but perhaps the best way for firms to play their part in cutting airline emissions is to start at home.

"Individual businesses have to consider their own role in climate change, and how they frame themselves as responsible businesses in that," says Dr Nicole Dando, a project manager at the Institute of Business Ethics. What might that mean in the world of transport? Video conferencing and taking low-emission travel options wherever possible seem the two best options.

While businesses mull these possibilities, the environment in Whitehall must be similar in some respects to the kitchens in Cranford, which borders Heathrow. As the rumble of environmentalist protests grows louder, you can just hear the civil servants smiling blithely as they attempt to stop pencils rolling off the desk and saying "After a while, you get used to it. You can't hear it at all."