“(1) The grant or refusal of an extension of time is a matter of judicial discretion to be exercised, not subjectively or at whim or by rigid rule of thumb, but in a principled manner in accordance with reason and justice. The exercise of the discretion is a matter of weighing and balancing all the relevant factors which appear from the material before the appeal tribunal. The result of an exercise of a discretion is not dictated by any set factor. Discretions are not packaged, programmed responses. “(2) As Sir Thomas Bingham MR pointed out in Costellow v Somerset County Council[1993] 1 WLR 256 , 263, time problems arise at the intersection of two principles, both salutary, neither absolute: ‘The first principle is that the rules of court and the associated rules of practice, devised in the public interest to promote the expeditious dispatch of litigation, must be observed. The prescribed time limits are not targets to be aimed at or expressions of pious hope but requirements to be met … The second principle is that a plaintiff should not in the ordinary way be denied an adjudication of his claim on its merits because of procedural default, unless the default causes prejudice to his opponent for which an award of costs cannot compensate.’”