25.—Where, of three or more concurrent wrongdoers, one is omitted from the claim for contribution, contribution shall be awarded to the claimant on the basis that responsibility for the damage is to be borne by the claimant and the contributor or contributors without regard to the responsibility of the omitted wrongdoer, and, in such a case, a claimant whose net remaining liability is increased or a contributor whose contribution is increased by reason of the fact that judgment has not been given against the omitted wrongdoer may claim contribution from such omitted wrongdoer in accordance with the provisions of this Part: but, where such last-mentioned claim for contribution is made by a contributor in respect of his own liability to make contribution and judgment is given in such contributor’s favour, execution shall not be issued on that judgment—

(a) except in accordance with the provisions of section 23, with the substitution of “contribution” for “damages” and of “original claimant for contribution” for “injured person” wherever they there appear, and “just proportion” in the said section being understood to mean for this purpose just proportion as between the contributor in whose favour judgment for contribution is now given and the wrongdoer against whom the said judgment is given, and in any case

(b) to an amount greater than the sum that, when added to the amount (if any) still due to the injured person, will equal the just proportion of the damages payable by the wrongdoer against whom the said judgment is given.