London 2012 security operation will vet 500,000 people

The Home Office is in the process of vetting half a million people to ensure there will be no breaches of security from anyone involved in the Olympic Games.

All employees, volunteers, competitors, officials and media from more than 200 countries will be screened.

A process that begun last October is now nearly two-thirds complete, with only around 100 applications so far refused, some of those on the advice of MI5. Among those remaining to be scrutinised are the extra security guards that have had to be recruited.

Tight security surrounded the torch relay in Northern Ireland after Monday's disruption. Today it will cross into the Republic, and will be paraded in Dublin.

A Home Office spokesman said: "We are undertaking stringent checks on all those seeking accreditation... We will leave nothing to chance in our aim to deliver a safe and secure Games."