British security officials are planning for the terror threat at this summer's London 2012 Olympics to be severe - meaning an attack is considered 'highly likely'.

Home secretary Theresa May is taking the responsibility of delivering a 'safe and secure Games', with the security budget already in excess of £1 billion.

"Like all Western countries we face a number of ongoing threats to national security," May told a conference on Olympic security.

"We face a real and enduring threat from terrorism and the Games, as an iconic event, will represent a target for terrorist groups.

"Our Olympic security plan has been developed against the assumption that the terrorist threat level will be severe.

"The terrorist threat has developed and evolved over the past few years and we have specifically designed a plan that is flexible and everything is under regular review.

"We are ready to take on the challenge of delivering a safe and secure Games, which uphold Olympic values and their ethos.

"We need an approach that is robust but seamless, visible but not intrusive, tough but intelligent.

"Our plans are well developed and on track and the International Olympic Committee shares that judgement. The Games must not only be an amazing spectacle, they must be safe."

Organisers of the Beijing Olympics were criticised for their heavy handed approach to security, with tanks parked prominently outside key venues and rows upon rows of unsmiling military patrolling every venue.

Cressida Dick, the Metropolitan Police's assistant commissioner for specialist operations, also wants the right balance to be struck, although the presence on the Thames of HMS Ocean, a helicopter carrier, will be an indication of intent.

"This is a sports event and we do not want it to be dominated by security. I think we have that balance right and we will have a fantastic Games," she said.

Sportsbeat / Eurosport