It shall be lawful for the promoters of the undertaking to purchase or redeem the interest of any holder of any security upon such lands the whole or part of which may be required for the purposes of the special Act, and that whether such promoters shall have previously purchased the right to such lands under burden of the security thereon or not, and whether the holder of such security be entitled thereto in his own right or in trust for any other party, and whether he be in possession of such lands by virtue of such security or not, and whether such security affects such lands solely, or jointly with any other lands not required for the purposes of the special Act; and in order thereto the promoters of the undertaking may pay or tender to the holder of such security the principal and interest due on such security, together with his expences and charges, if any, and also six months additional interest, and thereupon such holder shall immediately convey his interest in the lands comprised in such security to the promoters of the undertaking, or as they shall direct; or the promoters of the undertaking may give notice in writing to such holder that they will pay off the principal and interest due on such security at the end of six months, computed from the day of giving such notice; and if they shall have given any such notice, of if the party entitled to the lands under burden of such security shall have given six months notice of his intention to redeem the same, then at the expiration of either of such notices, or at any intermediate period, upon payment or tender by the promoters of the undertaking to the holder of such security of the principal money thereon due, and the interest which would become due at the end of six months from the time of giving either of such notices, together with his expences and charges, if any, such holder shall convey or discharge his interest in the lands comprised in such security, to the promoters of the undertaking, or as they shall direct.