Before I begin, I should declare a lack of interest. With just five days to go until the London 2012 Games, older readers may recall that I have always been an opponent of hosting this ludicrously bloated, epically expensive, hideously commercialised, sham amateur five-ring circus. I was, am and will remain not so much an olympiscep as an olympiphobe.

I implored Tony Blair's cabinet not to go for the Games and leave to Paris, Madrid or New York the pleasure of squirting away nearly £10bn on a lot of sports that are unpopular, some sports that aren't really sports at all and a few sports (think football or tennis) that are popular but are not played by the best in the world. I despaired when the Labour cabinet went ahead for no better reason than the then prime minister's anxiety that he would look a bit of a wuss if Britain didn't enter the bidding and on the basis of a few back-of-a-beer-mat sums about the costs, which were, of course, grossly underestimated.

Once the bid was won, though, I resolved to shut up about it. It is not attractive to be the curmudgeon griping from the corner when lots of other people look forward to enjoying themselves. Even as the build-up has confirmed everything that is wrong with the Olympics and everything that is mad about holding them in London, I have resisted the impulse to shout: I told you so!

Today, though, I am going to give in to the urge. Partly because we olympiphobes have been so richly vindicated. Partly because there may not be much time left to express dissent before we are charged with "crimes against the Olympic spirit" by Jeremy "stop grumbling" Hunt and Boris "put a sock in it" Johnson and incarcerated for the duration in an abandoned supermarket ringed by veterans of Afghanistan.

Let us remind ourselves of the claims made for the Games by the pro-Olympians. First, they said that it would showcase Britain to the world. London 2012 has indeed been generating headlines around the globe, headlines such as "No gold medal for security" in the New Orleans Times-Picayune and "London's show of farce" in the Vancouver Province as the rest of the planet has a chuckle at the inability of bungling old Brits to recruit enough security guards even when they've been given seven years' notice. The failure of G4S has been colossal, the company's performance as abysmal as its chief executive's attempts to explain himself before the home affairs select committee. Some questions are still to be answered also by the Home Office and Locog, the private company that contracted G4S and whose responsibility for £2bn of Olympic spend needs a rigorous audit.

Not content with showing the world the worst of our private sector, we are also advertising the worst of our public sector. The Public and Commercial Services Union, which represents thousands of border control staff, decides to call a 24-hour strike on the peak arrival day for visitors to the Games. Welcome, world, to Britain, a host nation in which a blitheringly incompetent private company and a bovinely led public sector union compete for gold in making a fool of your country.

The next big claim of the pro-Olympians was the vulgarly monetary one that the Games would make a profit for Britain. This is a line that David Cameron and his understrappers have been pushing hard in recent days as they try to justify to an austerity-strapped nation the cost of an event in which £27m will be blown on the opening ceremony alone.

The prime minister says that Britain "will make £13bn" from the Games, a figure calculated by statisticians at the Department of Wild Guesses, the Ministry of Thin Air and the Office of Think of a Number and Double It. The truth is that the Games rarely pay any tangible dividend for the host nation. Construction firms may turn a profit. The panjandrums who run the International Olympic Committee are very happy because they make vast sums from the TV rights. But the host nation almost always ends up well out of pocket after cost over-runs, the security bill and working days lost to Games disruption.

The "legacy" is only for those who are in love with white elephants. The future of the stadium is still moot. The Olympic velodrome is a handsome building for which no one can see a purpose after the Games. There will be some new housing in a previously derelict part of east London, but constructing an Olympic Park was a very expensive way of going about that. New York had regeneration projects as part of its bid and has gone ahead with them anyway – at a fraction of the cost.

As was predictable – and indeed predicted by those of us who examined the effect on previous host cities – the Olympics are having a baleful impact on London. Fearing traffic gridlock and oppressive security, residents flee. Some tourists come to watch the Games, but more are scared away. The Mall, Horse Guards and St James's Park have been in lock-down for weeks.

Every time I step in the London underground, I am assailed by posters and the booming voice of Boris warning Londoners to stay out of town during the period of Olympic occupation. And Lord Coe alone knows what fate may befall anyone caught in the vicinity wearing a T-shirt that is not approved by the corporate sponsors and the authoritarian jobsworths enforcing their branding rights. The siting of surface-to-air missiles in parks and on the top of flats completes the alluring city-under-martial-law look. It is like stepping into a dystopian future in which Britain is run by a military junta headed by Ronald McDonald.

London's shops, restaurants, bars, theatres, cinemas and concert halls are going to have a lean time of it during the siege. Hoteliers, who initially jacked up their room rates in greedy expectation of a Games windfall, are now frantically slashing prices to try to fill the many empty beds. The luxury hotels of Mayfair alone are happy because it is on their five-star beds that many of the VIPs and IOC bureaucrats will rest their pampered heads. Limousines swooshing along Soviet-style "Zil" lanes will whisk the Olympic nomenklatura across the city through traffic lights phased to green while working Londoners fume.

This was supposed to be "the People's Games". Why couldn't the Olympic bureaucrats stay at the Stratford Holiday Inn or take the rail line that they insisted was built? Ah, but that would mean rubbing shoulders with the poor saps who are paying for their privileges.

The most risible of the claims made by pro-Olympians is that the Games will inspire the host nation to become fitter. The heavy presence of McDonald's, Coke and Cadbury among the sponsors gives the lie to any notion that the Games are about promoting healthier lifestyles unless you suffer the delusion that a diet of cheeseburgers, liquid sugar and Mars bars will turn you into a rival to Usain Bolt. Studies of previous Games have found no evidence that they improve the host nation's health. Australians are no more sporty since Sydney 2000. The Los Angeles Olympics didn't make Americans thinner.

When every other claim collapses under scrutiny, the pro-Olympians have to fall back on the nebulous notion that being the host is somehow good for the national soul. Ministers have been rather desperately hoping that a few days of running, jumping and throwing will give an "Olympics bounce" to national morale or at least take our minds off the government's multiple troubles and the recession. So they will have been encouraged by an Ipsos Mori poll that reports that seven out of 10 respondents think the Games will lift the mood of the nation. I am prepared to concede that they might be right when the Games are on, but I very much doubt that any uplift to the nation's spirits will be enduring. The best study into what is known as the "hedonic effect" of big sporting events found that there was only one that sometimes could be said to make the host nation happier – the football World Cup. Hosting the Olympics has no long-term effect on a nation's sense of wellbeing.

I will now resume my silence on the subject before I am detained by the Olympic thought-police. I acknowledge that the Games will bring some transient thrills to those who watch them and more lasting satisfaction to successful competitors. I wish the best to our medal hopefuls to whom we now look to salvage some national pride. People who claim to be expert say that the United Kingdom has a very good chance of coming fourth in the medal league table. That would be impressive for a nation of 60-odd million people inhabiting some wet rocks in the north-east Atlantic. For all the blunders during the build-up, I have a hunch that the actual event will be largely successful. I hope so. Even an Olympiphobe doesn't want to give to the French the satisfaction of being able to crow that they would have done it so much better.