(1) Subject to the provisions of this section, the dismissal of an employee shall be deemed, for the purposes of this Act, to be an unfair dismissal unless, having regard to all the circumstances, there were substantial grounds justifying the dismissal.

(2) Without prejudice to the generality of subsection (1) of this section, the dismissal of an employee shall be deemed, for the purposes of this Act, to be an unfair dismissal if it results wholly or mainly from one or more of the following:

(a) the employee's membership, or proposal that he or another person become a member, of, or his engaging in activities on behalf of, a trade union or excepted body under the Trade Union Acts, 1941 and 1971, where the times at which he engages in such activities are outside his hours of work or are times during his hours of work in which he is permitted pursuant to the contract of employment between him and his employer so to engage,

(aa) without prejudice to paragraph (a), the employee -