Authority to allot — multi-class company (s.551)

A private company limited by shares has two classes of shares in issue: ordinary shares and non-voting preference shares. It adopted the unamended model articles and the articles contain no provision dealing with directors' authority to allot. The board wishes to allot further ordinary shares to raise capital and asks what authority is required before it can do so. Which of the following best states what the directors need before allotting the further ordinary shares?