An unlimited company having a share capital may by its resolution for re-registration as a public company under section 43, or as a limited company under section 51—
(a)increase the nominal amount of its share capital by increasing the nominal amount of each of its shares (but subject to the condition that no part of the increased capital is to be capable of being called up except in the event and for the purpose of the company being wound up), and
(b)alternatively or in addition, provide that a specified portion of its uncalled share capital is not to be capable of being called up except in that event and for that purpose.