Security preparations are a major part of the overruns and the concerns.
London 2012 will trigger the largest peacetime mobilization of British security forces in modern times, involving 50,000 troops, police, and private contractors. The number of soldiers exceeds Britain's deployment in Afghanistan.
An aircraft carrier will be parked in the Thames, and Typhoon fighter jets will be deployed in west London. On top of citywide cameras, police have access to unarmed drones for surveillance. Security screeners will confiscate liquids from spectators before they enter venues, and officials are warning of significant lines.
The Home Office insists, however, that the effort will be in keeping with a British tradition of understated security despite resonances with the US-led global war on terror.
"Any military resources will support but not supplant our police-led plans. Visitors to the UK can continue to expect to see the 'bobby on the beat,' not soldiers on the street," says James Brokenshire, minister for crime and security, by e-mail.
But, he says, "the UK is hosting the biggest and most high profile event in living memory" – so security agencies are leaving nothing to chance.