'The backgrounds of up to 500,000 people are being scrutinised in an unprecedented security screening designed to stop the Olympic Games being disrupted by criminals or terrorists, the Guardian has learned.

In what is understood to be the biggest vetting process since the second world war, the Home Office has so far refused about 100 applications for Games accreditation, mostly because of concerns about the extent of people’s criminal records.

However, some people have been denied accreditation on the advice of MI5, which has to assess whether a person might pose a significant threat to national security. The 500,000 figure includes anyone seeking employment at the Games, as well as athletes, coaches and officials from more than 200 competing nations.'

Read more: London 2012 Olympics Security Operation Investigating 500,000 People