And be it enacted, that if the promoters of the undertaking become possessed by virtue of this or the special Act, or any Act incorporated therewith, of any lands . . . F2 liable to be assessed to the poor’s rate, they shall from time to time, until the works shall be completed and assessed to such . . . F2 poor’s rate, be liable to make good the deficiency in the several assessments for . . . F2 poor’s rate by reason of such lands having been taken or used for the purposes of the works; and such deficiency shall be computed according to the rental at which such lands, with any building thereon, were valued or rated at the time of the passing of the special Act; and on demand of such deficiency the promoters of the undertaking, or their treasurer, shall pay all such deficiencies to the collector of the said assessments respectively . . . F2