Heathrow arguably had its third runway too early. In 1947, when commercial aircraft had just started using Britain's biggest airport, Heathrow had three runways. Now, only two remain, as room was needed to make way for Terminals 1, 2 and 3.

More than 60 years later, we have to decide whether a third runway should be built at Heathrow. But Heathrow has become a pawn in a political game. The decision should not be based on political point scoring or a kneejerk reaction to whoever shouts loudest, but on calm, detailed analysis of the facts.

The most important of those is that our desire to travel - whether for pleasure or work - is set to increase over the next 40 years. If a third runway isn't built at Heathrow, you can guarantee other airports will expand to meet that demand. The growth at Amsterdam, Frankfurt, Paris and Madrid, each of which already has three or more runways, shows little sign of slowing. Does the UK really want to shift the demand to fly - and the thousands of jobs that depend directly on the air travel business - to its European rivals?

Airlines will base their operations at the most competitive hubs in Europe. These airports will have more destinations for passengers to choose from and greater frequencies so that travellers can fly at times that suit them. More than a third of Heathrow's passengers are in transit - connecting from one airport to another via Heathrow. Some critics of BAA and Heathrow claim that an increase in such passengers is not in the national interest. They have missed the point.

Transit passengers are one of the prime reasons why airlines fly to so many destinations from Heathrow. If these passengers disappear, so would the choice of routes and the frequency, forcing passengers from London to fly via European hubs to reach cities in Asia and Africa. This transit traffic supports key routes, such as to Nairobi, Los Angeles and Bombay, giving greater opportunity for British passengers to travel there. And, of course, transit passengers, help to fill the planes: full flights are greener.

But, without a third runway, and with continued congestion at Heathrow, these passengers will want to transit via less-crowded airports outside the UK. If that happens, Heathrow's attractiveness would be dramatically reduced. Without such a diverse network, Britain would find itself increasingly isolated as a trading nation. Exports would slow and headquarters would be moved to vibrant countries that are investing in new capacity and infrastructure. Global corporations will turn their back on London in favour of better connected cities. Tens of thousands of jobs will be lost to France, Germany, Holland and Spain. There would also be a decline in the number of flights from regional UK airports such as Aberdeen and Belfast to Heathrow, contributing to the decline of regional economies.

Of course, a third runway shouldn't be built at any price. It is right that strict environmental criteria should be met before a go- ahead is given. But there is a sound environmental case for a third runway. If aircraft can land more promptly, hundreds of planes a day won't have to circle overhead for hours, each of them adding to emissions and noise levels. A new runway will reduce the dependency on the other two, particularly in poor weather conditions, when planes spend time on the ground wasting fuel, pumping out carbon emissions.

Delaying a third runway will not reduce net global greenhouse gas emissions; it will merely facilitate the growth of the continental European hubs, and even non-EU hubs outside the scope of emissions trading.

Let's imagine what air travel will be like in 2020, the earliest that a third runway could be operational. By then, many of the aircraft flying in our skies today will have been replaced. The next generation of planes will be even more advanced than the innovative aircraft that are now entering service, such as the carbon-fibre Boeing 787 Dreamliner and the Airbus A380. These aircraft are up to 30 per cent more fuel-efficient than anything flying today, and up to 60 per cent quieter. Just think what will be flying when a third runway is up and running.

Technology is moving on apace, both in design terms, efficiency and fuel type. By 2020 alternative fuels such as algae, which Virgin Atlantic is researching and developing with Boeing, may be commonplace. They are expected to produce no or vastly lower carbon emissions than today's environmentally unfriendly, expensive jet fuel.

It is remarkable that the South East of England has fewer runways today than in the 1940s. No wonder Heathrow is full to bursting. In the same way that the Tube and rail network are being replaced and extended, we need to transform one of the other main arteries - Heathrow. It is the only world-class hub that can support two main British carriers, Virgin Atlantic and BA, competing against each other to provide better choice and service for travellers.

Without a third runway, what incentive is there for airlines to invest in new planes and facilities at Heathrow? You can have the best customer service and cabin crew onboard, but if there is constant congestion and delay, then what is the incentive to operate out of the UK? If transit passengers are choosing Frankfurt or Paris, then perhaps UK airline operators should as well?

I am concerned that the prosperity of Britain may be held back by a lack of long-term investment in transport infrastructure. In other countries I see new, modern and efficient airports, few delays on take-off and landing, and real pride in the systems that carry consumers from A to B. So, let's stop stifling the UK's future growth and global reputation. Let's strengthen our competitiveness with a third runway. Without it, Heathrow will become a symbol of British decline.

Sir Richard Branson is president of Virgin Atlantic

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