If you were Tony Blair or George Bush, I presume you would contemplate sending in the army to liberate the benighted masses of such countries from their appalling regimes. Good idea. Get the tanks rolling down Whitehall and Pennsylvania Avenue right away! Because the countries concerned are Britain, the United States, Germany, France . . . and just about every “mature democracy” in the world (plus all the tinpot dictatorships, of course).

That, at least, is the accusation embedded in a book just published by Cambridge University Press. Life is too short to read every tome penned by Scandinavian and German social scientists. But Megaprojects and Risk, written by Bent Flyvbjerg, Nils Bruzelius and Werner Rothengatter, is a cracker. In lurid and startling detail it examines dozens of vast construction schemes around the world. Some were privately financed, but most drew heavily on the unwitting generosity of taxpayers. In the vast majority of cases the authors found that the costs were often double the estimates or more, the environmental damage far more extensive than anticipated and the demonstrable public “benefits” frequently half or less of what was promised.

Some of their examples are already classic chapters in the World History of Debacles. They include the Sydney Opera House — 15 times the estimated cost, and it still doesn’t really work as an opera house. Then there is Concorde, the world’s most famous superfluous supersonic airliner (12 times the estimated cost), and Boston’s “Big Dig” tunnel and road project, which is already $6 billion (£3.8 billion) over its $8 billion estimate, and they ain’t finished digging yet.

And naturally the authors devote many scandalised paragraphs to our own dear Channel Tunnel, which cost 80 per cent more to build than predicted and is now carrying about a third of the expected traffic. When Lord Grade was told how much his company was spending to make a film called Raise the Titanic, he quipped: “It would have been cheaper to lower the Atlantic.” Eurotunnel shareholders must feel that it would have been cheaper to drain the Channel.

At least other countries occasionally behave in a way which suggests that they have learnt from past mistakes. Take the Germans. Having watched in Teutonic disbelief as the costs on one high-speed rail link after another spiralled into the realms of the fantastical, they pulled the plug on the proposed Berlin-to-Hamburg line after learning that its estimated costs had doubled and its projected passenger figures had halved in five years.

By contrast, we British tend to plough on blindly, piling error on error. Flyvbjerg, Bruzelius and Rothengatter don’t even mention our most embarrassing megaproject muddles. We let the new British Library go almost £450 million over budget and 15 years behind schedule. We then virtually had to rebuild it from scratch after a quality-control team belatedly identified a staggering “230,000 items needing correction”. After that we proceeded to “invest” another half-billion in the Millennium Dome, grossly overestimating the public appeal of this off-white elephant. It’s still costing us £250,000 a month to keep empty, incidentally.

Now we are embarking on a similarly grandiose scheme to rebuild Wembley at a cost that appears to be many times in excess of any other football stadium in the known universe. And this week Scottish taxpayers are digesting the news that the projected cost of their new Parliament has soared yet again, to £400 million. The original estimate was £40 million. If there were ever to be a Megalomaniac League of Mismanaged Megaprojects, the British would be champions this year, next year, every year.

But Flyvbjerg, Bruzelius and Rothengatter aren’t into nationalist point-scoring, thank goodness. What fascinates them is what they call the “paradox” of megaprojects. These gigantic schemes — for dams, tunnels, suspension bridges, new towns, high-tech military systems — are the most important and expensive ventures that countries or private consortia will ever undertake. Yet time and again they are nodded through on the basis of information that proves to be hopelessly wrong, and then supervised and scrutinised with a cavalier lightness of touch. Your patio extension probably underwent a more rigorous cost/benefit analysis than the British Library ever did.

Environmental snags — usually overlooked or deliberately downplayed in initial presentations — frequently prove to be the biggest reason for cost overruns. The authors cite the hilarious (unless you are German) instance of the high-speed Hannover to Berlin rail link, which was originally routed close to the breeding area of rare bustards, then rerouted underground (at an estimated cost of £10 million for each bustard life this would have saved!), and then rerouted again, making the journey time considerably longer and greatly reducing the consequent passenger demand.

Of course, the out-of-control megaproject is not a new phenomenon. When the Suez Canal opened in 1869 its final cost was 20 times higher than the first estimate. The construction of New York’s magnificent Brooklyn Bridge claimed 27 lives and cost twice what it was supposed to do. “That’s an awful lot of trouble just to get to Brooklyn,” quipped music-hall comedians of the day. Charles Barry’s Houses of Parliament overran its budget by 200 per cent. Work on Wren’s St Paul’s Cathedral was so extended and costly that Londoners had to pay a special coal tax to get it finished. Doubtless Hadrian had to grapple with dreadful overspends on his Wall, too.

But the fact that megaprojects’ costs have been consistently underestimated since time immemorial is seized on by the authors as evidence that factors more sinister than simple arithmetical incompetence are at work. They argue that mankind is perfectly capable of learning from bitter experience in other fields. So our apparent inability to predict accurately either the cost of megaprojects or their subsequent usefulness must be caused by something else.

What is it? Some megaprojects are clearly folies de grandeur. Defying rhyme or reason, they have been irresistibly propelled by powerful politicians intent on creating monuments to themselves. I call this the Ozymandias Complex, as in “Look on my works, ye mighty, and despair” (though the case of the Millennium Dome was rather more of an Ozymandelson Complex).