“All that is required is to reverse the procedural irregularity. A reversal of this procedural irregularity [he said] would then cause that substantial injustice - namely [to pay the interest be removed]. In my judgment it cannot be possibly arguable that it would cause substantial injustice to the Claimant if the procedural irregularity were reversed and the correction of the howler prevented, if so doing, would cause, on the one hand, a substantial injustice to the Defendant and, on the other, a wholly undeserved windfall to the Claimant”