Lord (Sebastian) Coe, chairman of the London Organising Committee of the Olympic Games, has warned spectators of rowing and equestrian events that their viewing areas are a sea of mud and advised raincoats. One of his officials - presumably one of little faith regarding Ra - went a step further: ''Bring wellies (gumboots).''

Then there is travel, or lack thereof. London's traffic moves like molasses on a normal day. Its underground train system is already so jammed at peak hour that fuming commuters must let trains go without boarding them because there simply is not room to squeeze on. Some stations close for a while on exceptionally bad days, keeping commuters from even getting on to a platform. But the system will have to cope with about a million extra trips per day during the Olympics. Londoners are being asked to work from home or find other ways to stay off the system for the duration.

This week, road traffic into London slowed to a crawl as parts of the 48 kilometres of dedicated Games Lanes - to be used only by members of the ''Olympic Family'' - came into operation. An accident and a suicide caused two separate bottlenecks with traffic not moving at all for about 45 minutes. Other jams were caused by last-minute braking as drivers fearing fines in the Olympic lane suddenly swerved to change lanes.

All these difficulties are tiresome, particularly for the gloomier Londoners who already viewed the Games as an ordeal to be endured with the kind of British stoicism displayed during the Blitz. But they are minor and predictable problems.

The chaos around Olympics security, however, is of an entirely different order. It opens the way to catastrophe. Over the past 10 days, Britain and the world learned that the Games has a shortfall of 3500 security guards, as well as problems notifying the guards who do exist about when and where they are to report for work. Only 30 out of an expected 300 security officers turned up to guard cyclists. Only 10 out of 58 arrived to guard footballers; only 20 out of 58 at the main Olympic hotel; and no guards at all turned up for an induction day at Coventry Stadium (70 had been expected). ''On a daily basis it's a lottery as to how many staff are going to turn up,'' Clive Chamberlain, chairman of Dorset Police Federation, told the Guardian. ''It's a fiasco, an absolute debacle.''

Home Secretary Theresa May, at the centre of a political firestorm over the mess, claims the government knew nothing of the crisis until it was told last week by G4S, the company hired to provide Games security. She has called in 3500 emergency troops, including sailors and airmen, and police from eight forces around the nation to fill the shortfall.

Another 2000 might be needed but the government is fending off that further embarrassment, despite warnings from defence chiefs that notice is required if their troops are to be in action by the opening ceremony next Friday. This would bring the total numbers of military staff involved in the Games, both planned and unplanned, to 19,000.

GS4's chief executive Nick Buckles endured a grilling by MPs this week in which he admitted that he couldn't guarantee he could supply even the 7000 guards now required by his tattered end of the bargain. He said he could not predict the scale of ''no shows'' until recruits failed to respond to an email. He also could not promise that all the guards would speak fluent English: ''I don't know what fluent English is.''

Asked by an MP whether the debacle was a ''humiliating shambles'' for his company, Buckles admitted, ''I would have to agree with you.'' G4S has seen £400 million wiped off its market value and is predicting it will incur a £50 million loss on the Games contract. But it is still insisting on claiming its £57 million ''management fee''.

How did it come to this?

It appears computer glitches at G4S sent recruits to the wrong venues or otherwise supplied them with incorrect schedules. There also seems to be a larger than expected number of casual employees who have lost interest or found another job. But May claimed the company had been assuring ministers it would ''overshoot'' the recruitment targets in its £284 million contract. This is at odds with an internal Home Office memo revealed this week by the Sunday Times that warned in April, ''We will very soon start to see big shortfalls against planned numbers.''

Part of the problem is due to governmental dithering. Last December, a full six years after London won the Games, the government had a last-minute rush of blood to the head over security issues and dramatically amped up the brief to G4S from 2000 guards (in a contract signed in December 2010) to 13,700 guards.

The tardiness was despite the fact that London was hit by the 7/7 suicide bomb attacks the day after winning the race for the Olympics in 2005.

Defence chiefs had offered to provide Games security but the government decided outsourcing to a private company would be better.

Margaret Hodge, chair of the Commons public accounts committee, said, ''It is outrageous. [The organisers] knew in 2005 that security was going to be a major challenge but they left it too late.''

There have also been concerns about the quality of recruits. G4S, which won the contract partly because it has previously provided security for the Olympics site during construction, has also protected the Wimbledon tennis championships.

A security consultant who went undercover for the company at Wimbledon last year wrote a report listing alarming lapses.

These included some staff lacking even ''the most basic security knowledge'' having to guard a significant terrorism target; staff routinely leaving premises unprotected by sleeping on the job; and some recruits being allowed to skip hearing and smell tests designed to check that they were able to notice fires or explosions.

The security consultant who wrote the report, Peter Bleksley, is a former Scotland Yard detective. He warned that the problems could ''eventually prove catastrophic for G4S'' and some were so serious they could have ''fatal consequences'' if they were not fixed before the Games.

Buckles claims those concerns were taken on board and dealt with, but one whistle-blower has claimed the company has been forced to resort to a ''no-fail policy'' for recruits in the current crisis.

G4S made headlines in the 1990s over security breaches with its prisoner-escort service. This week, prosecutors decided not to bring charges against three of its guards who restrained an Angolan man at Heathrow who became ill and died of cardio-respiratory failure following the incident in October 2010.

Despite the torrent of bad publicity, Games chief Coe has promised that safety is not compromised: ''My responsibility is to make sure that we get a Games that is safe and secure. We will do that, and it is to make sure that our teams, the Home Office and the military sit alongside G4S and mobilise and deploy exactly who we need to.''

Assistant Commissioner Chris Allison, the national Olympic security coordinator, has also denied that security is falling over: ''The plan is exactly the same as it was. It is just being delivered by different people. I went through the search regime at Olympic Park … and it was everything you could possibly want.''

It will certainly be one of the most militarised Olympics ever, with missiles poised and jets on hand and the Royal Navy's largest warship deployed to launch military helicopters.

All that might prove of little use if a would-be terrorist slips through the net at Heathrow Airport. The Observer reported that terror suspects had been able to enter Britain in the run-up to the Games without being picked up by security checks. A senior border officer claimed inexperienced recruits were repeatedly failing to refer passengers on a watch list to counter-terrorism officers.

For those trying to organise the London Olympics, the blame games are already up and running.