The discussions on nuclear capabilities in the Estonian capital, Tallinn, came as Nick Clegg, the Liberal Democrat leader, once again declared that his party would consider scrapping the £80bn Trident submarine fleet although he held out the possibility of switching to a different, cheaper, nuclear deterrent.

Mr Rasmussen said: "Each individual ally has the right to take decisions themselves but there is a political contribution to the consensus to consider as part of an integrated defence." It was important, he added to "take decisions based on consensus, taking into consideration the concerns of others so that we maintain alliance unity and move together". Mr Rasmussen avoided referring directly to Britain in outlining the responsibilities of Nato members on the nuclear issue

The US Secretary of State, Hillary Clinton, refused to be drawn into the Trident issue. "We have to let the British people and their government make their own decisions on nuclear deterrents," she said. However, she stressed, as long as nuclear weapons exist, Nato will remain a nuclear alliance. "And as a nuclear alliance, sharing nuclear risks and responsibilities widely is fundamental."

Mrs Clinton added that it was the Obama administration's "broad aim" to continue to reduce the role and number of nuclear weapons in its overall arsenal. She called on the allies to broaden deterrence by pursuing territorial missile defence – in contrast to regional or global missile defence. The US arsenal contains about 5,000 strategic, or long-range, nuclear weapons – including about 3,000 that are in storage.