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In international law a Head of State, Head of Government or Foreign Minister may sign a treaty in his or her own right. Any other person signing a treaty on behalf of a State needs to produce the authority from one of the three above to do so – known as 'Full Powers'.

In UK practice, the Queen does not sign treaties herself, although the Prime Minister sometimes does. Full Powers are normally given by the Foreign Secretary, except for certain EU treaties which are drawn up as between Heads of State, and therefore require a Full Power from the Queen. FCO Ministers, and certain UK Representatives, hold general Full Powers, which give them the authority to sign any treaty – although this is always subject to the approval of the Foreign Secretary in each case. For anyone else to be able to sign a treaty, a specific Full Power must be produced for that person (or persons) and that treaty alone.

The Full Powers document is drawn up by Treaty Section and – unless it is for signature by the Queen – is submitted by the lead FCO department to the Foreign Secretary for signature. Government Departments other than FCO will therefore need to approach the appropriate FCO department to request Full Powers. They should provide the name, title, position and any decorations of the person to be named in the Full Powers, and if possible attach a copy of the treaty concerned. Full Powers can take time to produce, so wherever possible this should be done well in advance of the proposed date of signature of the treaty.

Full Powers are not required for a treaty in the form of an Exchange of Notes. However, a non-FCO Minister or official should not sign without the specific authorisation of the Foreign Secretary or another FCO Minister.

| Instruments of Ratification | Glossary of Treaty Terms |
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