“The biggest concern has always got to be a safe and secure Games,” Cameron told a press conference with the Olympic Stadium as a backdrop. “That matters more than anything else.

British PM David Cameron

“I think we’ve made as many preparations as we can. I think we have very good contingency plans in place.

“Always as prime minister I feel that is an area I should take personal responsibility for.”

London's security preparations had been called into question in comments by Republican candidate Romney, who is in London to attend the opening ceremony today.

Romney said several issues in the build-up to the Games had been “disconcerting”, focusing on a fiasco involving private security contractor G4S which has failed to provide the number of private guards it had promised.