Britain must not choose between Europe and the United States, Lord Robertson has said.

Speaking in London on Monday night, the outgoing NATO secretary general argued that close relationships with both the EU and US were vital to global security.

"Britain can no more choose between Europe and America than you or I can choose between food and drink," he said.

"We need both. As Europe needs the US, so the US needs Europe. The differences between Europe and the United States are no more fundamental than those within Europe or within North America. They show that our family is strong enough to agree to disagree.

"They differentiate NATO and the EU from the Warsaw Pact and Comecom, and from the terrorist fanatics who detest debate and use suicide bombers to kill the innocent instead of arguments to sway the undecided."

Delivering the English Speaking Union's annual Churchill lecture, the former defence secretary argued five "characteristics of the 21st century" - instability, overspill, terrorism, failed states and the proliferation of weapons of mass destruction - created a "guaranteed supply chain of disorder".

"They add up to a security environment in which threats can strike at any time, without warning, from anywhere," he said.

"Threats that could vary from a terrorist with a box-cutter on an airline to a chemical weapon mounted on a ballistic missile. Threats that nobody can confidently predict.

"The good news is not only that there is agreement within Europe and across the Atlantic about this analysis, but that we also agree on how to respond.

"There is no chasm between unilateralists and multilateralists. Nor is there an unbridgeable gap between Atlanticists or europhiles."

Robertson agreed with the prime minister that a stronger European Union would not weaken NATO.

"Only if the result is a Europe with no more soldiers and no more modern equipment, but more unnecessary headquarters and complicated wiring diagrams with nothing at the end of them, will I be sceptical," he said.