Tony Blair agreed yesterday that there could be circumstances in which he would order the captain of a Trident submarine to pull the nuclear trigger switch.

"I don't think it is ever sensible for a prime minister to forecast those circumstances", the Labour leader said. "I believe in the nuclear deterrent."

Asked how he felt about the "awesome" responsibility which, he would carry if he became the next prime minister with Labour committed to keeping Trident, he replied: "I regard it as - awesome."

Introducing his section of the Labour Party's foreign and defence policy document, A Fresh Strategy for Britain, yesterday, David Clark, the party's defence spokesman, said: "We will retain the British nuclear deterrent, Trident. When satisfied with verified progress towards our goal of a global elimination of nuclear weapons, we will ensure British nuclear weapons are included in such negotiations."

Meanwhile, Dr Clark said, Labour would continue the present Government's commitment to limit the number of British Trident warheads to 192 - three per missile on four submarines. Labour will also remain committed to Nato, to building up the role of the Western European Union as its European arm, oppose plans to give the European Union a military role, and continue to offer the United Kingdom's services for international peace-keeping.

Its most radical proposals related to the reform of the United Nations and increasing its ability to respond to crises quickly, including enlargement of the Security Council - of which Britain is one of the five permanent members - reforming the UN Secretariat and a greater role for the UN in co-ordinating international economic, environmental and social policy.

Robin Cook, the shadow Foreign Secretary, stressed the interdependence of foreign and security policy and foreign aid. "We make a big mistake if we imagine that foreign policy is less important to Britain because we are no longer a global power. It is even more important for our prosperity and security in the modern world that Britain pursues an active foreign policy. If Britain is no longer an imperial power then it is all the more important that we safeguard our security through alliances and maintain our influence through partnerships."

Robin Cook said that "there must be a broadening of the [UN] Security Council to make it more representative of the world". Asked whether Germany should get a permanent seat, he said there was "certainly a respectable case" to be made, but that an additional German seat would increase the existing imbalance in favour of old European powers.

The document repeated Labour's cautious formula that a single European currency "could produce significant benefits", while omitting the Labour leadership's usual qualification that it would require the consent of the British people either in a referendum or a general election.

And, after a fierce internal battle between Joan Lestor, spokeswoman on development issues, and Gordon Brown, the shadow Chancellor, it contained a promise only to "start to reverse the decline in UK aid spending", with no timetable.

9 A Fresh Start for Britain: Labour's Strategy for Britain and the Modern World.