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separate Customs territory for which it has international responsibility possesses full autonomy in the conduct of its external commercial relations and of the other matters provided for in this Agreement, and that its acceptance does not relate to such territory ; and provided further that if any of the Customs territories on behalf of which a contracting party has accepted this Agreement possesses or acquires full autonomy in the conduct of its external commercial relations and of the other matters provided for in this Agreement, such territory shall, upon sponsorship through a declaration by the responsible contracting party establishing the abovementioned fact, be deemed to be a contracting party. 5. (a) This Agreement shall enter into force, as among the Governments which have accepted it, on the thirtieth day following the day on which instruments of acceptance have been deposited with the Secretary-General of the United Nations on behalf of Governments signatory to the Final Act the territories of which account for eighty-five per centum of the total external trade of the territories of the signatories to the Final Act adopted at the conclusion of the Second Session of the Preparatory Committee of the United Nations Conference on Trade and Employment. Such percentage shall be determined in accordance with the table set forth in Annex H. The instrument of acceptance of each other Government signatory to the Final Act shall take effect on the thirtieth day following the day on which such instrument is deposited. (b) Notwithstanding the provisions of subparagraph (a) of this paragraph, this Agreement shall not enter into force under this paragraph until any agreement necessary under the provisions of paragraph 2 (a) of Article XXIX has been reached. 6. The United Nations is authorized to effect registration of this Agreement as soon as it enters into force. Article XXVII Withholding or Withdrawal of Concessions Any contracting party shall at any time be free to withhold or to withdraw in whole or in part any concession, provided for in the appropriate Schedule annexed to this Agreement, in respect of which such contracting party determines that it was initially negotiated with a Government which has not become, or has ceased to be, a contracting party. The contracting party taking such action shall give notice to all other contracting parties and, upon request, consult with the contracting parties which have a substantial interest in the product concerned. Article XXVIII Modification of Schedules 1. On or after January 1, 1951, any contracting party may, by negotiation and agreement with any other contracting party with which such treatment was initially negotiated, and subject to consultation with such other contracting parties as the CONTRACTING PARTIES determine to have a substantial interest in such treatment, modify, or cease to apply, the treatment which it has agreed to accord under Article II to any product described in the appropriate Schedule annexed to