The keys to Wembley Stadium - the venue for nine Olympic football matches - have gone missing.
The cost of replacement has not been disclosed, but is thought to run into tens of thousands of dollars.
It is an embarrassing security blunder that may be the fault of the police, the BBC reports.
Scotland Yard said internal security keys for Wembley Stadium were reported missing last Tuesday.
The keys were being used by officers to search the venue as part of the Olympic policing operation.
Specialist police teams were called in to locate the keys, but they could not be found. Detectives said there was no evidence they had been stolen.
The Games' organisers Locog said that, as a result, locks at the venue had to be changed.