§ Llew Smith
To ask the Secretary of State for Foreign and Commonwealth Affairs which international treaty994W to which the United Kingdom is party (a) gives legal underpinning to the possession of nuclear weapons by the United Kingdom and (b) permits the modernisation of the United Kingdom's nuclear weapons of mass destruction. 
§ Mr. MacShane
The United Kingdom is recognised as a Nuclear Weapons State in accordance with the definition in Article IX(3) of the Nuclear Non-Proliferation Treaty.
The UK is satisfied that its possession and maintenance of its minimum nuclear deterrent is in compliance with international law.