8A person who is not qualified under paragraph 6 above may act in respect of any accounting period as auditor of a trade union or employers' association if—
(a)it was registered under the Trade Union Acts 1871 to 1964 on 30th September 1971 ;
(b)he acted as its auditor in respect of the last period in relation to which it was required to make an annual return under section 16 of the [1871 c. 31.] Trade Union Act 1871 ;
(c)he has acted as its auditor in respect of every accounting period since that period ; and
(d)he is for the time being authorised by the Secretary of State under section 161(1)(b) of the [1948 c. 38.] Companies Act 1948 otherwise than as mentioned in paragraph 6 above.