A certificate bearing an Apostille stamp was issued by a nation that is a signatory to the UN Hague Convention. The Foreign, Commonwealth and Development Office (FCDO), which authenticates the origin of a UK document for use in another nation, is the only issuing authority/government office. When the necessary conditions are met, an Apostille certificate will be provided when the FCDO certifies the authenticity of the presented document. You must next legalise the passport through an embassy, consulate, or high commission if you intend to use it in a nation that is not a signatory to the Hague Convention.