Plans for an airport on the Thames Estuary have been around almost since the invention of the airplane. So let’s not get too carried away by the latest reincarnation, says Alastair Stewart

Shergar will win the Grand National, ridden by Lord Lucan, and Elvis will triumph on X-Factor before an airport is ever built in the Thames Estuary. Or so it would seem: every few years for the past six decades journalists have breathlessly reported ambitious plans for airports near to or off the Kent or Essex coastlines destined to “supplant Heathrow”. But so far, the only take-offs and landings have been by the estuary’s birdlife.

If a third runway is not built at Heathrow, the UK will muddle along, with business people moaning, column writers mourning another lost opportunity and holiday makers slowly edged out

Far more years ago than I care to recall, as a junior reporter on this magazine, I excitedly drafted an “exclusive” on a planned new airport linked by maglev rail lines to an equally long-since defunct mini-city on Essex’s Rainham Marshes. “Isn’t that the old Maplin airport?” my editor scoffed. “I was writing about that when I started in journalism. It won’t happen.”

Hydra-like, as each hair-brained scheme is lopped, an even more extravagant one emerges several years later. Thus, we have had: Cliffe in Kent (variously proposed and dropped since 1946); Maplin Sands (devised in 1971, abandoned in 1974); Isle of Sheppey (artificial island 1990s, sunk without trace 2002); and Shivering Sands, or “Boris Island”, north-east of Whitstable, which has been the subject of not a little media derision.

The latest offering, unveiled to fanfares by Lord Foster and Halcrow, envisions four runways on a platform straddling the Isle of Grain and the estuary, 24/7 high-speed rail links to London, an orbital rail network round the capital, flood barriers, submerged tidal generators and lots of other whizz bang stuff. And a price tag of up to £50bn.

There are two fundamental obstacles to building a new airport in the South-east: economic (they cost a lot and the country’s bust) and political (the proposed flight paths will fly over lots of voters, many in key marginals). Cynics might suggest the latter has swayed government policy: the coalition has ruled out a third runway at Heathrow and second ones at Gatwick and Stansted (all largely surrounded by Conservative constituencies). So what chance grassroots support for a brand new behemoth from “Basildon man” and his neighbouring constituents on either side of the estuary?

However, the latest reincarnation seems to have apparently garnered more support. Having Lord Foster as the mastermind gives the “Thames hub” proposals more gravitas. Exciting graphics were reproduced lavishly in most of the quality papers.

Hydra-like, as each hair-brained scheme is lopped, an even more extravagant one emerges several years later

Critically, the FT argued, new transport secretary Justine Greening has campaigned strongly against the expansion of Heathrow. (But a relevant factor may be she’s the MP for Putney, straight under the flight path, reinforcing the view that politics has more clout than transport considerations.)

More encouragingly, “senior sources” let it be known the scheme had won the support of Downing Street and the Treasury. However, the £5bn of investment in infrastructure unveiled in the chancellor’s autumn statement omitted any mention of the hub or any specific plans to expand existing airports, focusing instead on “shovel ready” road and rail projects.The more ambitious longer-term projects that the government supports, but does not want to fund, will rely on the private sector, including pension funds and overseas government wealth funds.

There definitely appears to be huge potential interest from private sector investors for long-term infrastructure (torpedoing the latest batch of headlines generated from within the Treasury that “PFI is dead”). But investors much prefer projects that have more definable income streams and building costs, such as schools and hospitals, than ones that rely on traffic risk, especially as complex and grandiose as the hub.

Heathrow to many (myself included) is a nightmare. But it is easier and less prohibitively expensive to make it a bigger, three runway nightmare than create a brand new megalith in the Thames.

The new scheme’s backers point to modern wonders such as Hong Kong’s Chek Lap Kok and the new Doha international airport - both built on reclaimed land. But both regions have considerably deeper pockets and somewhat less democratic approach to planning. Ultimately, if a third runway is not built at Heathrow, the UK economy will still manage to muddle along, leaving business people to moan, column writers mourning another lost opportunity and holiday makers being slowly edged out.

It would be nice to see horrid Heathrow replaced by a shining new beacon. But like most transport white elephants, it won’t fly.

Alastair Stewart is a construction analyst