Invalid marriages

19. A marriage shall be declared invalid where-

(a) at the date of the marriage one of the parties is already married;

(b) at the date of the marriage either party to the marriage would be prohibited from marrying by reason of the provisions of section 6 or 7:

Provided that, where consent is required for the marriage under the first proviso to subsection (1) of section 6 and a marriage has taken place without such consent, such marriage shall not be declared invalid if, in the meantime, the female party concerned-

(a) completes her eighteenth year;

(b) obtains the required consent; or

(c) is pregnant.