Prime Minister Gordon Brown says Britain could reduce its nuclear arsenal as part of a global disarmament deal to persuade Iran and North Korea to give up its nuclear ambitions.

Speaking to reporters at the G8 summit in Italy, Mr Brown said Britain may reduce its warhead numbers in return for Tehran and Pyongyang abandoning nuclear programmes.

But he stressed Britain had no plans to unilaterally abandon its 160-warhead Trident arsenal or scrap plans to replace the fleet of submarines that act as its platform.

"Iran is attempting to develop a nuclear weapon, Korea is attempting to develop a nuclear weapon," he remarked.

"We've got to show we can deal with this by collective action and I think unilateral action by the UK would not be seen as the best way forward.

"What you 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."

Mr Brown - who first offered to negotiate on Trident as part of international talks in March - gave no details of the size of any cut in the British deterrent.

He said that in future, he would like to see a nuclear policing regime where "the onus will be on the countries that don't have nuclear weapons to prove they don't have nuclear weapons."

Group of Eight leaders meeting at their summit in Italy agreed to US President Barack Obama's proposal that a nuclear security summit should be held in Washington ahead of the planned review of the Non-Proliferation Treaty.