Britain today issued a renewed appeal for countries to come together and combat the threat of a nuclear terrorist attack.
Foreign Office minister Alistair Burt said the number of incidents involving the loss or theft of nuclear materials around the world was growing and nations needed to show the "utmost vigilance".
Opening a two-day international symposium in London, he said the threat had been considered sufficiently realistic for nuclear detectors to be deployed over the summer at the Olympic Games.
"Nuclear terrorism is a real and global threat. A successful attack, no matter where in the world it came, would be catastrophic," he said.
"Catastrophic for the immediate devastation and terrible loss of life, and for the far-reaching consequences - psychological, economic, political and environmental.
"Such an attack was unthinkable just a generation ago. But it is now a possibility we need to confront with the utmost vigilance."
According to figures released by the UN watchdog - the International Atomic Energy Agency - between 1993 and 2011 there have been 2,164 cases recorded of nuclear material "outside state control".
Of those, 147 occurred in 2011, with four involving the highly enriched uranium needed to build a nuclear bomb.
Mr Burt said the threat meant Britain's Cyclamen system, used to detect nuclear and radiological materials at ports and airports, was deployed at the Olympics.
"At the Olympic Park, yes, absolutely, processes were deployed... that would trigger the equipment so that we would know something was passing through," he said.
He also expressed concerns that some governments were helping terrorists acquire nuclear materials or expertise - although he refused to be drawn on the countries involved.
"It wouldn't be right to identify individual nations who may be engaged in helping or assisting," he said.
Register for free to continue reading
Registration is a free and easy way to support our truly independent journalism
By registering, you will also enjoy limited access to Premium articles, exclusive newsletters, commenting, and virtual events with our leading journalists
Already have an account? sign in
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies