The British Prime Minister Gordon Brown is offering to scale back Britain's nuclear deterrence if an international agreement is reached to cut the world's nuclear arsenals. Mr. Brown is expected to tell a special session of the United Nations Security Council on Thursday that he'll be willing to give up one of four royal navy submarines that carry Trident nuclear missiles. Officials are insisting that cost isn't a factor here. Here's our defence correspondent Nick Childs. Gordon Brown is saying he'll be ready to throw part of the trident force into the port in the context of a much bigger global disarmament deal. He said so in general terms before. This offer though is more concrete. There is a growing sense that to avoid what some fear could be a sudden cascade of new nuclear states, the established nuclear powers need to do more in terms of disarmament to keep the proliferation regime intact. The Prime Minister will hope his move will be seen as an important gesture. But the key to the process will be the actions of the big players, the United States and Russia.