“Ten days to the Games — what could go wrong?” a sarcastic headline in Britain’s Guardian newspaper asked Tuesday. The answer, as this Olympic host nation has discovered, is: Quite a lot.

Even as athletes begin arriving in London for the 2012 Summer Games, Olympic organizers are coming under fire over bungled security staffing and other issues that have prompted the British media and opposition lawmakers to already declare the event a “fiasco.”

On Tuesday, organizers said they would withdraw half a million tickets for soccer matches and reduce stadium sizes because of scant demand in farther-flung host cities including Glasgow and Cardiff. A day earlier, U.S. and other athletes were hauled around for hours on at least two buses that lost their way en route to the Olympic Village in East London.

That joy ride, however, paled in comparison with the security blunders casting a shadow ahead of the Games. The private contractor hired to provide guards — British giant G4S — conceded last week that it was at least 3,500 personnel short, sending the military scrambling to make up the gap. On Tuesday, furious lawmakers summoned the company’s chief executive, Nick Buckles, before Parliament for an emergency hearing. They grilled him on management failings and reports that even more G4S staffers were ill trained or were failing to report to work at Olympic sites across Britain, forcing police departments to step in to provide additional security in some areas outside London.

“It’s a humiliating shambles for the country, isn’t it?” said David Winnick, a member of the opposition Labor Party.

Buckles replied, “I cannot disagree with you.”

Meanwhile, the press issued fresh diatribes against Olympic traffic planning in London, where dedicated lanes for Olympic-related transport were reportedly confusing motorists and complicating what is already one of the world’s busiest rush hours. Many drivers appeared not to realize that most of the newly labeled lanes could still be used until next week.

But at least one major transit spot was getting relatively high marks — Heathrow Airport, which had its busiest day ever Monday as athletes began pouring in. Heathrow is notorious for its long immigration lines, particularly as border control staffing has been cut in recent months. But on Monday, officials said, the maximum wait time for the more than 236,000 arriving passengers was about 24 minutes.

“We have spent seven years preparing for the Games’ challenge,” said Nick Cole, head of Olympic planning with the British Airports Authority. “Now we are putting that planning into action with thousands of extra staff and volunteers on hand to welcome the world to London.”

That did not help the athletes assigned to the buses that got lost on the way to Olympic Park. Kerron Clement, a U.S. 400-meter Olympic hurdler, was not amused, tweeting: “athletes are sleepy, hungry and need to pee. Could we get to the Olympic Village please.” and, “Um, so we’ve been lost on the road for 4hrs. Not a good first impression London.”

Thus far, though, the security shortfalls have caused the biggest stir — not just because of their magnitude but because of their disclosure so close to the Opening Ceremonies.

The company has said it stands to lose up to $50 million from its contract because of the failures. The government, meanwhile, has sought to reassure the public, national athletic delegations and the media that the military is well prepared to ensure that security requirements will be met.

“Our troops are highly skilled and highly trained and this task is the most important facing our nation today,” Home Secretary Theresa May said in a statement after the shortfalls became apparent.

“There remains no specific security threat to the Games and the threat level remains unchanged,” she said.

Eliza Mackintosh contributed to this report.