The United Kingdom (UK) is responsible for the Crown Dependencies and British Overseas Territories in international law. The long-standing practice of the UK when it consents to be bound by a treaty, is to do so on behalf of the United Kingdom of Great Britain and Northern Ireland and any of the Crown Dependencies or Overseas Territories that wish the treaty to apply to them. It is also possible for treaties to be extended to dependencies and territories at a later stage. Once a treaty has been extended to any dependency or territory, its provisions will similarly apply to them as with the UK, unless the contrary is specifically stated in a particular case. In certain circumstances, the Crown Dependencies and the British Overseas Territories may be authorised to conclude their own treaties by a process of entrustment.

The OECD Convention has been extended to the Bailiwick of Jersey and Bailiwick of Guernsey, the Isle of Man, Gibraltar and Bermuda on 20 July 1990. This means that the OECD Convention applies to these dependencies and territories and they are part of UK for the purpose of its membership of the OECD. OECD Decisions and Recommendations apply to the same extent to these dependencies and territories as they do to the UK.

When the UK ratified the OECD Convention on 2 May 1961, it did not specify what territorial application should be given to the Convention. To clarify this situation, the Ambassador of the United Kingdom in France wrote as follows to the French Minister of Foreign Affairs, Mr. Roland Dumas on 20 July 1990:

"... I have the honour to draw your attention to the Convention on Economic Co-operation and Development signed in Paris on 14th December 1960 and ratified by the Government of the United Kingdom of Great Britain and Northern Ireland on 2nd May 1961, and to inform you that the United Kingdom Government hereby certifies that the said Convention applies to the Channel Islands, the Isle of Man, Gibraltar and Bermuda. I am addressing a copy of this letter to the Secretary-General of the Organisation for Economic Co-operation and Development...".

The Head of the UK Delegation to the OECD also wrote to the Secretary-General as follows:

"... We (...) have formally transmitted [the above] declaration to the Government of France (...). Accordingly, I can confirm that future decisions and recommendations adopted by the Organisation under Article 5 of the Convention shall extend to those territories specified in the Declaration unless the contrary is specifically indicated in a particular case. Furthermore, the obligations to which the UK has subscribed under past decisions and recommendations, including those in the Codes of Liberalisation, will also apply to those territories under the same conditions as currently apply to the UK...".