TMA 1970, s 20(8A)

(a) that the notice relates to a taxpayer whose identity is not known to the inspector or to a class of taxpayers whose individual identities are not so known;
(b) that there are reasonable grounds for believing that the taxpayer or any of the class of taxpayers to whom the notice relates may have failed or may fail to comply with any provision of the Taxes Acts;
(c) that any such failure is likely to have led or to lead to serious prejudice to the proper assessment or collection of tax; and
(d) that the information which is likely to be contained in the documents to which the notice relates is not readily available from another source.

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