(1) Copyright in a literary, dramatic musical or artistic work is not infringed by an act done at a time when, or under an arrangement made at a time when—
(a) it is not possible by reasonable inquiry to ascertain the identity of the author; and
(b) it is reasonable to assume—
(i) that the copyright has expired, or
(ii) that the author died 50 years or more before the beginning of the calendar year in which the act is done or the arrangements are made.
(2) Subsection (1)(b)(ii) does not apply in relation to work in which copyright originally vested in an international organisation by virtue of section 154 and in respect of which an order under that section specified a copyright period longer than 50 years.
(3) In relation to work of joint authorship—
(a) the reference in subsection (1) to its being possible to ascertain the identity of the author shall be construed as a reference to its being possible to ascertain the identity of any of the authors; and
(b) the reference in subsection (1)(b)(ii) to the author having died shall be construed as a reference to all the authors having died.