You don't need a weatherman to know which way the wind blows. A week ago as the chattering classes and psephologists were digesting Boris Johnson's dethroning of Emperor Ken and the wider wipeout of New Labour in the local elections, an arguably equally large shift in the landscape of Britain was being delivered by Shell.

For last week the oil supermajor that has been seen as a friend to big investment in the search for renewable energy dealt the UK wind energy industry its biggest kick in the turbines in its short history.

The decision by Shell director Linda Cook to quit the flagship London Array windfarm in the Thames, a monster project of 300 turbines the height of Nelson's Column sitting in the estuary and capable of producing 1000 megawatts of electricity - a quarter of the capital's needs - has changed the face of green energy in the UK, if not irrevocably then at least for the foreseeable future.

Shell was a one-third partner in the project with the giant German power company E.On and Danish wind specialist Dong Energy.

When first seriously mooted four years ago, London Array was hailed by the Government and the environmental lobby as real evidence of - aptly - a revolution in the future of windmills.

But a couple of years ago the Evening Standard was the first to report flaws in the project: E.On was getting windy over the soaring costs of the project, which was then delayed because nimbies in Kent argued they did not want it in their back yard. And now, in the year when the first watts were supposed to be generated by the turbines, the project lies in tatters as Shell says it wants no more to do with it.

The decision - allied with the recent disclosure that BP wants to sell off $7 billion of renewable interests - is seen as the signal that Big Oil, with crude at $120 a barrel, wants to go back to searching for big oil finds.

Not so, says Shell, which argues it is concentrating on its wind interests in the US (where the subsidies are even better and where the place is so big you don't have people telling you to get off their land).

So Shell has given up on wind in the UK then? Not so, again, says Shell, a company that could make $40 billion profit this year, it is just the economics of this project that do not work.

Campbell Dunford has been a longtime critic of wind, saying its capabilities have been overblown compared with other green power sources. But the chief executive of Renewable Energy Foundation says Shell's decision and the grave doubts over the future of London Array are a sad day for the industry.

"We are disappointed," he said. "We have long argued that wind has been oversold and that expectations have been raised far too high but at least with this project it was going to be offshore and in a large grouping.

"It was meeting the objectives of harnessing more wind, generating more power and delivering closer to where the load is needed."

But while Shell has declined to give a detailed explanation of its decision, Dunford says a stack of negatives has forced its hand.

"It not only reflects the supply chain constraints in the industry - the fact that the US and China are sucking in all the available kit - it indicates also the rising costs, of the steel for the turbines, of the construction, the cost of connection to the grid and the copper wires, and even shows how the weakening of the pound against the euro has mounted up," he said.

"It also reflects what is now becoming more apparent as the first windfarms around the country go into production - that the maintenance costs of these offshore installations are higher than originally feared."

Dunford calculates that using the electricity spot price currently at £45 per megawatt/hour and with the size of ROCs subsidies available in the future - the renewable obligations certificates-that we, the consumers, are funding-through higher power prices to incentivise windfarm builders - the partners in London Array could have expected to be paid up to £130 for every mw/hr unit produced.

AS DUNFORD says: "If Shell, with all the money they are making every year and with all the subsidy available, say they can't make the numbers work, then something is wrong. Just ask yourself a question: if you are sitting in a financial institution in the City of London and are asked to invest in the industry now, would you? Shell's decision impacts every other project in the country."

The British Wind Energy Association sees it differently. "Consortia come together and then often regroup at various stages of project development," said Maria McCaffery, BWEA chief executive.

"This is common in the wind industry and has happened many times already. We expect to see a great deal of interest in taking over Shell's share in the London Array."

Hmmm. As the poet said: the answer, my friend, is blowing in the wind.