Whenever I've been sailing, I've found the wind pretty unpredictable. A ruddy big storm one minute and then, as soon as you've got the hang of it, the sails flap, the wind's gone and the boat doesn't move for hours.

I know you're probably not interested in my nautical adventures - even though it's been said I bear an uncanny likeness to Captain Birdseye - but the ministers who've just approved the world's biggest wind farm in the Thames Estuary should be. Because in their rush to blanket our wonderful countryside and now the seascape with thousands of these infernal turbines - many of them higher than St Paul's cathedral - they seem to have overlooked the simple fact that wind does not blow every minute of the day.

Yes, it might sometimes feel like it when you're out there in your boat in the Thames Estuary - where a consortium including the likes of Shell are now almost certain to build 341 turbines over 90 square miles of sea, a site as big as 23,000 football pitches. 

Damaging

But the reality is, these socking great turbines 12 miles off Kent and Essex, between Margate and Clacton will spend most of their life idle. Standing 600ft tall and with vast `wingspans' to catch whatever breeze there might be, they'll work for only 30 per cent of the time at best - because the wind won't be blowing all the time. Now that would not be a problem if we could store all the electricity produced when it's really stormy to be used in the lean times when the sea is calm. But there is no plan to do that, and anyway it would be prohibitively expensive. So this vast wind farm, this wonderful green solution to our energy supply that Ministers have set their hearts on, will have to have the back-up of conventional power for the times when nothing's blowing out at sea. If it doesn't, the lights, kettles, TVs - and everything else in the million or so homes the consortium claims the turbines will power - will be switched off when the wind dies down.

You might think that, as a lifelong conservationist, I would be in favour of wind turbines. And even though they are big, ugly and hugely damaging to wildlife, you'd be right - if they did what they were supposed to do.

But since they don't - and since they need conventional power as a backup anyway - they aren't in any way helping to conserve our environment. Quite the reverse.

If the government has its way, the most beautiful and wild landscapes in the uplands of Britain will continue to be desecrated by these monstrosities.

As a Dutch electrical engineer with vast experience of wind farms said recently: `It seems strange that promoters of wind energy never mention the significant disadvantage of wind energy: namely, its complete unreliability.

`One might justifiably suspect that a hidden personal or political agenda is at play here.'

He's right - there is a political agenda. In the Queen's Speech last month, Britain's first Bill to combat global warming made it a legal requirement for future governments to slash greenhouse gas emissions by 60 per cent by 2050.

To help achieve this, an Energy White Paper will be published in March to boost renewable technology, such as wind and tidal power.

So enthralled is our government by wind turbines that it has made sure they are subsidised to the tune of hundreds of millions of pounds, while all the time pre­tending that electricity produced by these new satanic mills is not only the answer to all our environmental ills but also cheap.

This `green' subsidy comes in the very complicated form of `Renewable Obligation Certificates' or ROCs.

The electricity industry has to supply a certain percentage from renewable sources. If they fail to reach their target --which is currently about five per cent but growing - they are fined by the energy watchdog, Ofgen. 

Soaring

For every megawatt hour of energy produced from a renewable source, the industry receives a ROC from Ofgen as an incentive. These ROCs are then bought on the open market - along with the electricity itself - by the distribution companies for approximately £45 per megawatt hour. The effect is to double the wholesale price of electricity, which these distribution companies send on to our homes.

And who is paying for all of this? You and me, in our soaring electricity bills. It's the stealth tax no one is talking about because, so far, the government has managed to keep it quiet. Experts I know in this field have worked out that the Thames Estuary project will receive approximately £153 million per year in ROC subsidy.

According to the Commons public accounts committee, the total cost of subsidies paid to renewable energy suppliers could reach £5 billion by 2010. By any standards, that is a vast amount of money. Let me be clear. I am all for renewable energy. I can get very passionate about generating the energy of tomorrow. My own per­sonal favourites are tidal power and concentrated solar power - vast farms of mirrors in the hot deserts of North Africa and Arabia could produce huge amounts of electricity that could be sent to Europe easily and cheaply. It is vital that we improve energy conservation, too. Why isn't the Government putting more money into subsidising loft insulation or energy-saving lightbulbs? 

Inefficient

Think of it this way: given the current number of wind farms, just two long-life bulbs used in every one of the 25 million households in the UK would save as much energy as all the turbines in this country are now producing.

It would be far more sensible for the Government to buy 50 million long-life light bulbs and hand them out across Britain than to throw all this money at wind farms. Windfarm supporters are abound with tales of how much carbon dioxide emissions they cut.

But because wind speeds in this country are so variable; because the turbines themselves are so inefficient; and because fossil or nuclear-led back up will be necessary, the savings in carbon dioxide emissions are noth­ing like they're cracked up to be.

Indeed, the Government's own figures show that even if they meet their target, global carbon dioxide levels would fall by an amount so insignificant as to be barely measurable, let alone having any impact on climate change.

We need to be told whether the industry is economically viable without the subsidies it receives. We need to be told whether the manufacture of a turbine farm - up to the point when the blades start spinning-actually creates more carbon dioxide than it saves.

Because without all that vital information, we're sailing against the wind.