Britain has began an inquiry into security at the London Olympics after a worker reportedly smuggled a fake bomb onto the site.

The worker carried the artificial bomb through two checkpoints without being searched by security staff, according to a British tabloid newspaper report.

Once inside, he was able to drive the package through the site, taking it past the velodrome before posing for a photograph with it outside the Olympic Stadium, The Sun reported.

The stunt, 24 hours before 40,000 people attended the official opening of the stadium on Saturday, was designed to show how vulnerable the site, which also includes the athletes' village, could be to a terrorist attack.

To date, organizers have spent $1.6 billion on security for the games including 23,700 guards, 14,000 troops at key times and an 11-mile electric fence.