2012 London Summer Olympics Airspace Guide: There are specific procedures that must be followed if you are intercepted by a military aircraft. As a last resort, if you fail to comply with the procedures or you fail to comply with the directions of the military aircraft, you may be considered a threat to security which may result in the use of lethal force. 
http://olympics.airspacesafety.com/media/9639/airspace_guide_june_26.pdf