The dustup began Wednesday, as Romney, who ran the 2002 Salt Lake City games, said there were "disconcerting" signs in the days before this year's games.
"The stories about the private security firm not having enough people, the supposed strike of the immigration and customs officials — that obviously is not something which is encouraging," he told NBC News.
"Do they come together and celebrate the Olympic moment? And that's something which we only find out once the games actually begin," he said.
Cameron soon rebuked Romney. "We are holding an Olympic Games in one of the busiest, most active, bustling cities anywhere in the world. Of course, it's easier if you hold an Olympic Games in the middle of nowhere," he said*.
"I think we will show the whole world not just that we come together as a United Kingdom, but also we're extremely good at welcoming people from across the world," Cameron added. "I will obviously make those points to Mitt Romney. I look forward to meeting him."