For 25 years the NPT has been the linchpin of nuclear disarmament efforts and is the only internationally accepted document to enshrine as its goal the eventual elimination of all nuclear weapons.
Douglas Hurd, the Foreign Secretary, welcomed the agreement as "a victory for common sense". Robin Cook, the Labour foreign-affairs spokesman, called on the British government to act on its pledge to pursue nuclear disarmament.
In Kiev, where President Bill Clinton stopped off following his summit meeting in Moscow with President Boris Yeltsin, the UN decision to extend the NPT was hailed by the US President as "a critical step" in making the world safer and more secure.
A jarring note was sounded by one nuclear-club member, France, which made clear it would probably have to carry out more nuclear weapons tests to maintain a credible deterrent until it develops simulation techniques.
There was no immediate reaction to the NPT accord from President Yeltsin, who has been preoccupied with his summit with Mr Clinton this week.
Tension at the conference between the five declared nuclear- weapons states - Britain, France, the United States, Russia and China - and the non-nuclear nations, was largely defused by compromise proposals tabled by South Africa that led to the adoption of separate documents reaffirming and strengthening the main commitments expressed by the NPT.
There was spontaneous applause in the General Assembly chamber as the conference chairman, Yayantha Dhanapala, ambassador of Sri Lanka, dropped his gavel, announcing that the decisions to prolong the treaty and to approve the appended declarations were adopted without a vote.
Though there was little doubt that a formal show of hands would have produced the simple majority required to prolong the treaty, it was feared as many as 20 non-aligned states, unconvinced that the nuclear powers were moving quickly enough towards disarmament, would oppose extension. Their objection would have damaged the treaty's future credibility.
At the eleventh hour, Arab states asked for a resolution expressing concern over Israel's nuclear-weapons capability and its refusal to sign the NPT. The resolution, also adopted and sponsored by Britain, the US and Russia, calls for a "Middle East zone free of nuclear weapons as well as other weapons of mass destruction". It does not name Israel, because three countries in the region - Oman, Djibouti and the United Arab Emirates - are not NPT signatories either.
Though not legally binding, the appended documents are likely to have long-lasting consequences, not least for Britain. There is also a text requiring that the current five-yearly reviews of how the NPT is implemented be conducted almost annually, and a declaration of principles restating each of the treaty's most important obligations, especially on nuclear disarmament.
The declaration calls, most importantly, for a "programme of action" towards disarmament and the "determined pursuit by the nuclear-weapon states of systematic and progressive efforts to reduce nuclear weapons gradually". This is certain to be used to bring pressure on Britain and France, the two nuclear-weapons states that have refused to put their nuclear arsenals on the table in global arms-reduction negotiations. The declaration commits the nuclear-weapons states to completing, by the end of next year, negotiations for a comprehensive nuclear test ban and the "early conclusion" of talks on a convention to ban the production of fissile materials for weapons use.
A footnote to the conference has been South Africa's emergence as a leader of the developing countries. The declaration of principles, which made consensus possible, was based on proposals tabled by Pretoria at the start of the conference. "It would be impossible to overstate the importance of the contribution they have made," a delegate said.