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To some, it is the perfect antidote to the frustration experienced by millions of Heathrow passengers each year and the misery of those who endure the drone of jet engines passing over their homes.
A new airport built at sea that is easy to reach, passenger-friendly and doesn't keep anyone awake at night.
For others, it is an idea so far-fetched and outdated that it should be laughed out of court.
London Mayor Boris Johnson, who has described Heathrow as "a planning error of the 1960s", is reviving a radical idea: phasing out Heathrow and replacing it with a new airport on an artificial island in the Thames estuary.
He has given a team at City Hall and a group of engineering consultants the task of re-examining the concept.
"This study will look at the whole feasibility of an estuary airport," said a City Hall insider. "The mayor wants to rule it in or out once and for all."
The new airport has already been given a variety of labels: "Boris Island", "Heathrow-on-Sea", and the favourite tag of former Transport Secretary Ruth Kelly, "Fantasy Island".
But though the idea of replacing one of the world's busiest airports may seem fantastic, plans for building a new hub in the estuary have existed for 40 years.
The mayor envisages building the airport on reclaimed sandbanks 3.2km off the coast of Sheerness, Kent, in waters 3m to 4m deep.
It would have four runways and could be expanded to six, dwarfing the capacity of Heathrow's two fully operational runways.
Planes would take off and land over the sea, solving the blight of noisy engines at Heathrow and allowing the airport to operate around the clock.
Connecting the island to London and the continent with high-speed rail links would allow passengers to reach the capital in just over half an hour, the same as it takes to get to Heathrow.
The mayor's plans are loosely based on Hong Kong, where a HK$20 billion ($4.6 billion) project on an artificial island took six years to complete. Johnson's biggest obstacle, unsurprisingly, is money.
Land reclamation and investment in roads and railways add billions to the bill. The plan produced five years ago predicted a cost of £31 billion ($88 billion). Boris Island could need as much as £40 billion.
The sheer expense would have seen it kicked into the long grass long ago, were it not for one thing - Heathrow.
London's main airport has been derided as a monument to Britain's make-do-and-mend approach to planning. It opened in 1946 from an army surplus tent and had to wait until 1955 for its first permanent building. Since then, it has grown piecemeal while the capital has sprawled around it. "Heathrow has been a disaster in terms of planning and simply expanding it further would be typical of the way governments have tried to solve our aviation problems," said Sir Peter Hall, president of the Town and Country Planning Association and author of an influential 2006 pamphlet calling for the airport to be retired.
While Johnson is plumping for a spot off the Isle of Sheppey, another blond Tory, former Prime Minister Sir Ted Heath, preferred Maplin Sands off Foulness Island. But Heath's plan, conceived in the 1960s, was abandoned because of lack of money.
The last time the Government took a look at the idea was in 2003. Several proposals were dismissed as too expensive and ecologically damaging. Ministers also said birdstrike posed too great a risk to planes.
Those involved in the proposals believe the Government was too quick to dismiss them. "It is not pie in the sky," said Mark Willingale, who led Thames Reach, one of the schemes considered. "The mayor is right to start this debate again."
But the Labour Government's determination to push ahead with a third runway is one of the worst kept secrets in Westminster. Kelly used her final speech as Transport Secretary to rubbish the mayor's big idea.
"Boris may find his Fantasy Island airport a useful device to distract from the Tories' divisions on Heathrow," she said last month. "I call it politically opportunistic, economically irresponsible and environmentally disastrous."
The support of business lies with expanding Heathrow. Its leading cheerleader is British Airways, which has a stranglehold over existing take-off slots. For the airlines, expanding Heathrow is the cheapest option.
But an estuary airport might attract money from foreigners. Possible backing is already being sought from China.
Moving London's main airport would have the advantage of freeing up prime real estate in West London. Town planners predict 30,000 homes could be built on Heathrow's land.
An estuary airport could create as many as 200,000 jobs in London's impoverished east.
However, the proposed location is close to the wreck of the SS Richard Montgomery, which sank in 1944 packed with explosives.
But those concerns won't stop the army of Heathrow passengers trekking to their plane or residents plagued by noise from hoping that Johnson's Fantasy Island will one day become real.
BORIS' BIG IDEA
What: London Mayor Boris Johnsonis considering a plan to build a replacement airport for Heathrow.
Where: 3.2km off the coast of Sheerness, Kent.
On: Reclaimed sandbanks in water 3 to 4m deep.
With: High-speed rail and ferry links to the city.
Cost: As much as £40 billion ($112 billion).
- INDEPENDENT
