LONDON — Britain offered its first accounting of its nuclear arsenal Wednesday, revealing that it has a stockpile of 225 warheads in a move that offers transparency to non-nuclear states in hopes of winning stricter global controls on the spread of atomic weapons.The announcement, made without fanfare in the House of Commons, follows the Obama administration's disclosure that the United States has stockpiled 5,113 nuclear warheads and "several thousand" more retired warheads awaiting the junk pile — the first description of the secretive arsenal born in the Cold War and now shrinking rapidly.The US made the announcement at the May 3 opening of a five-year review of the Nuclear Nonproliferation Treaty, considered the cornerstone of global disarmament efforts, where Washington and its allies are seeking stronger measures to prevent the spread of nuclear arms. Britain made its announcement as the monthlong conference nears an end on Friday, with intense debate under way on a final document.William Hague: This will assist in building a climate of trust"We believe that the time is now right to be more open about the weapons we hold," Foreign Secretary William Hague told the House of Commons. "We judge that this will assist in building a climate of trust between nuclear and non-nuclear weapons states and contribute, therefore, to future efforts to reduce the number of nuclear weapons worldwide."Britain had earlier revealed that it possessed 160 operational warheads, but Hague's comments that the country's "overall stockpile of nuclear warheads will not exceed 225 warheads" was the first time the maximum size of the total stockpile was revealed. The Foreign Office later said the 225 figure was the number of warheads the country now holds.Countries that don't possess nuclear weapons have long demanded more openness from the nuclear-weapon states — the US, Britain, France, Russia and China — about the size and nature of their arsenals as an essential step toward nuclear disarmament, which is a key plank in the Nuclear Nonproliferation Treaty. British Foreign Office Minister Alistair Burt told a briefing for UN reporters that Hague sent him to New York as the treaty review conference nears an end to emphasize the importance of the announcement in the House of Commons."We are very conscious that everything relating to nonproliferation depends on confidence, the confidence between those who are parties to the treaty, those who are nuclear weapon states and those who are not," he said.The new British government is also conscious that, over the last decade, the treaty had come under pressure with no outcome from the 2005 review conference, Burt said."We wanted to make an immediate and positive contribution to that process," Burt said.For that reason, Burt said that Hague announced "two particularly strong confidence-building measures" — the maximum number of warheads in Britain's stockpile and a review of the government's policy on the use of weapons.Burt cites UK's 'determination to be open and transparent'On the nuclear arsenal, Burt said, "until this moment that number has always been kept secret.""The foreign secretary has today revealed that number openly as part of our determination to be as open and transparent as a nuclear weapon-holding state in this process," he said. On the policy review, he said, Britain's position has always been that "the use of nuclear weapons would only be in the most extreme circumstances of self defense following attack in certain particular circumstances."Hague has now offered "a review and a discussion" of that policy, Burt said.