Britain’s Trident nuclear deterrent could be thrown into a world disarmament deal after President Obama called yesterday for the biggest summit to stop the spread of atomic weapons.

In a move designed to increase pressure on Iran, up to 30 countries will be invited to Washington next spring for a nuclear security conference.

Iran is likely to be forced to prove to the world that it does not have a nuclear weapons programme, Gordon Brown suggested at a press briefing last night.

His words raised the prospect of inspectors visiting Tehran to verify the existence of weapons. Officials suggested that a refusal to provide evidence could lead to pariah status for Iran, pointing out that Libya had been admitted to the world community after renouncing a nuclear programme.

He said that a successful non-proliferation agreement could be followed by multilateral negotiations in which reductions to the Trident nuclear arsenal would be put on the table.

G8 leaders backed Mr Obama’s decision to call the summit before the planned review of the NonProliferation Treaty (NPT). He wants to build on the success of his trip to Moscow, where both countries agreed to reduce their nuclear stockpiles by 500 warheads.

Mr Brown said that in the next few days he would set out recommendations for a framework for a deal that could be reached next year. This is expected to envisage nuclear-armed powers reducing their arsenals and offering assistance to non-nuclear states to develop civil atomic energy in return for assurances that they will not build a bomb.

The Prime Minister said there was no question of Britain offering unilaterally to abandon its 160-warhead Trident arsenal or scrap plans to replace the fleet of submarines that act as its platform.

He told reporters: “Iran is attempting to build a nuclear weapon. North Korea is attempting to build a nuclear weapon. We have got to show we can deal with this by collective action.

“Unilateral action by the United Kingdom would not be seen as the best way. What we need is collective action by the nuclear weapons powers to say that we are prepared to reduce our nuclear weapons, but we need assurances also that other countries will not proliferate them.”

It is not yet clear which countries will be invited to the summit in Washington but Mr Brown expects Britain to be there.

His offer to put Trident on the table as part of a serious multilateral arms reduction negotiation was first made in a speech in March in which he said: “As soon as it becomes useful for our arsenal to be included in a broader negotiation, Britain stands ready to participate and to act.”

Mr Brown is coming under increasing pressure from Labour backbenchers to cut his planned multibillion investment in Trident as part of the cutbacks in government spending.

He described nuclear proliferation and the danger of nuclear material falling into the hands of terrorists such as al-Qaeda as “one of the big issues of the world”.

He added: “When the Non-Proliferation Treaty was signed there were five nuclear weapons states. Now there are nine and the possibility of Iran, North Korea and others may seek to acquire nuclear weapons. We will have a big rise in nuclear weapons states in this decade.”

Iran is a signatory of the NPT.

Despite the summit agreeing a climate change initiative this week the 17-nation Major Economies Forum failed to agree on a carbon dioxide reduction target for developing countries.

Ed Miliband, the British Energy and Climate Change Secretary, welcomed the deal on keeping warming to a 2C (3.6F) rise but said world leaders needed to be more ambitious.

He told The Times: “Of course there is still a lot more hard work that needs to be done. There needs to be more ambition from both developed and developing countries, most importantly for the mid-term targets for 2020.

“But this agreement significantly increases the chances of the kind of deal we need in Copenhagen. It defines the framework in which the negotiations will take place.”

Mr Obama said that the global recession made it harder to strike an international agreement to fight dangerous temperature increases, but he urged emerging economies that rejected specific clean-energy goals to fight the temptation toward cynicism and embrace them soon.

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