In the two years since Prime Minister Gordon Brown asked him to review how best to protect crowded places, transport and national infrastructures from terrorist attacks, measures have been taken which have "made the nation safer but we are not safe - the threat is still there", he told a conference on security for the 2012 Games at at the Royal United Services Institute in Whitehall.

The former First Sea Lord of the Royal Navy said: "We are not complacent.

"We do not underestimate the scale of the Olympics challenge.

"There is no doubt that the 2012 Olympic and Paralympic Games promises to be the greatest Games in history and possibly the greatest security challenge the UK has faced since the Second World War."

The current risk is substantial but may be severe by 2012, he said.

An Olympic strategy has been developed to try to address the issues.

West said: "It is risk-based and intelligence-led and provides flexibility to respond to any challenges should the need arise."

The "huge complexity" of risks includes not just the terrorist threat but also serious and organised crime, domestic extremism, crowd management and natural disasters such as flooding and heatwaves.

The 2012 summer Games will be staged as other regular events in the British calendar - such as Wimbledon and the Notting Hill Carnival - go ahead as normal, each requiring their own security.

The aim is not to go over the £60 million security budget, West said.

He said: "We in the UK have a magnificent track record of hosting events - it's one of the reasons that we won the Games."


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