If at any time the authorized capital is divided into different classes or series of shares, the rights attached to any class or series (unless otherwise provided by the terms of issue of the shares of that class or series) may, whether or not the Company is being wound up, be varied with the consent in writing of the holders of not less than three-fourths of the issued shares of that class or series and of the holders of not less than three-fourths of the issued shares of any other class or series of shares which may be affected by such variation.