The protesters who have made fools of parliamentary and airport “security experts” are right, even if they don't understand climate change and can't spell. Building a third runway at Heathrow is “Plane Stupid”.

The arguments for running down Heathrow have nothing to do with the contribution of aircraft to global warming, which is so small as to be completely irrelevant. For moral reasons we should encourage flying, which is an essential component of the globalisation process that is spreading prosperity to developing countries and making the world a more peaceful and tolerant place.

Why, then, do I support the protesters? Because expanding Heathrow would be environmental, economic and political madness for four powerful local reasons that have nothing to do with saving the Earth.

The first argument against expanding Heathrow is its geographic location. People in Britain's aviation business have long kept a dirty little secret to themselves. Heathrow is the only main urban airport that lies on an east-west axis relative to the city it serves. This is a problem because prevailing winds in much of the world blow from west to east, meaning that runways have to be aligned in this direction and aircraft using Heathrow must take off and land over densely populated parts of London.

Most other big urban airports - Charles de Gaulle in Paris, JFK in New York, O'Hare in Chicago, Schiphol in Amsterdam - are north or south of the cities they serve. As a result, their main runways point towards open country and cause far less nuisance than Heathrow does. It is this accident of geography, rather than the inherent Nimbyism of the British public, that probably explains why Heathrow has provoked so much more opposition than airports in other large cities around the world.

But what about London's three other main airports - Gatwick, Stansted and Luton? They all lie north or south of the main conurbation. Why then are they so underused? The standard answer is that they are harder to reach from Central London and serve fewer destinations; but this is a symptom of underdevelopment, rather than the cause. If Stansted and Gatwick were better airports with fewer delays, less chaos and faster rail links to London, they would become more popular. And the more Heathrow became congested the greater the advantages of the other airports would grow.

The reason why this hasn't happened is obvious: BAA owns Heathrow, Gatwick and Stansted and has every incentive to stifle, rather than intensify, competition to Heathrow.

The next reason to oppose further development at Heathrow, therefore, is that competition would provide a far less expensive and more reliable solution to London's airport problems. Many of today's delays at Heathrow are caused not by capacity shortages but by chaotic baggage services, broken-down boarding tunnels or shortages of security equipment and staff. Experience, from the privatisation of Britain's utilities to the breakdown of communism in Russia, shows that inefficiency is much more likely to be eliminated through competition than more investment. It is stupid even to raise the question of extra runways - never mind answer it - until the BAA monopoly is broken up.

Suppose, however, that BAA was broken up and London's airports started to operate in competition. What if airlines, British Airways in particular, still wanted more capacity at Heathrow for extra flights? We would then have to ask who all these extra flights would be for. Would they serve mainly passengers to and from southeast England? Or would they be designed to turn Heathrow into a global “hub”, with passengers flying in from all over Europe merely to change planes and then fly out to other parts of the world?

The “economic case” presented in the government White Paper on Heathrow expansion is fairly clear - British Airways wants to create a global “hub and spoke” network centred on Heathrow.

This raises the third reason for opposing Heathrow expansion. Even if it were true that BA's commercial future depended on flying millions more transit passengers in and out of Heathrow, it is not at all clear why this would serve Britain's national economic interest. Transit passengers spend almost no money in Britain, yet their flights create pollution, congestion and energy waste. What is good for BA is not necessarily good for Britain. But closer inspection of this “economic argument” suggests that developing Heathrow's “hub” status might not even be beneficial for BA.

The hub-and-spoke business model assumes it is more efficient to put passengers on feeder flights in and out of a huge hub airport instead of flying them straight to their destination. This model was developed in the 1950s by Federal Express. Fedex found that it could move parcels more efficiently from New York to Washington by flying them 1,000 miles from New York to Memphis and then back 800 miles to Washington, rather than shipping them directly from New York to Washington by road. US passenger airlines all rushed to copy the Fedex model when they were deregulated in the 1980s, but this proved a ruinous mistake. It turned out that people were not parcels. Missed connections at hubs created huge resentments and inefficiencies, and these contributed to the bankruptcy of almost every big US airline.

European airlines, undaunted by this fiasco, have all rushed towards the same business model in the past decade, but again the main result has been a wave of bankruptcies or near-failures, including Swiss Air, Alitalia and KLM. Meanwhile, the world's most commercially successful airlines - Ryanair, easyJet, Virgin Atlantic and SouthWest in the US - have all eschewed the hub-and-spoke model, instead offering point-to-point services directly to their passengers' destinations. It is quite likely, therefore, that any expansion of Heathrow that encouraged the hub-and-spoke business model would actually be commercially suicidal for BA.

That, of course, is a decision that ought to be taken by the company itself. But if BA wants to create a global hub-and-spoke service it should bear the full environmental costs. In the case of Heathrow, the environmental costs of adding millions of transfer passengers are bound to be immense. There is, however, an alternative. London is lucky enough to have an ideal site for a vast new airport that could eventually replace Heathrow and become a genuine international hub. An artificial island in the Thames estuary, far enough away not to create any noise pollution problems but easily connected to the centre by a high-speed rail link, has been the best answer to London's airport requirements since the Government adopted this solution back in 1971, only to abandon it later on the ground of cost. At the time it seemed too much of an engineering and financial challenge.

But since then, such island airports have been successfully, and profitably, constructed in Hong Kong, Japan and many other places - and could be part-funded by gradually selling off the land at Heathrow.

A rational airport policy for London must begin by creating competition between Heathrow, Gatwick and Stansted by breaking up the BAA monopoly. Only then will we know whether extra airport capacity is really needed. And if new capacity is needed, the place to build it is the Thames estuary - allowing Heathrow eventually to be closed.

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