[A] judgment or order that expressly reserves to parties a leave or liberty to apply can be varied on an application pursuant to such leave only so far as may be necessary for the purpose of working out the actual terms of the order so as to make it more efficacious in matters of detail. What is meant in this context by 'working out' the terms of an order is considered in some of the cases on the point. In Cristel v Cristel [1951] 2 KB 727, 728, Somervell LJ said it 'involves matters on which it may be necessary to obtain the decision of the court. Prima facie, certainly, it does not entitle people to come and ask that the order itself shall be varied'. A simple judgment for a money sum requires no 'working out' in any sense, so that liberty to apply is quite inappropriate in such a case. On the other hand, there are many orders, particularly on the equity side, as to which the process of carrying the primary judgment into effect may require supervision, with the consequence that further or supplementary orders or directions may be needed to enable it to achieve its purpose. An example commonly encountered in practice is specific performance, where, because the consent or approval of some person or instrumentality may be needed to authorise a preliminary step, the judgment sometimes takes the form only of a declaration that the contract be specifically performed, together with subsidiary orders compelling particular acts to be done. See Egan v Ross (1928) 29 SR (NSW) 382, 388; Hasham v Zenab [1960] AC 316; Brown v Heffer [1967] HCA 40; (1967) 116 CLR 344, 350. The primary order may then need to be supplemented by further orders from time to time before the stage is reached at which the defendant can finally be ordered to perform specifically what he contracted to do in the way of transfer or payment as the case may be: Brown v Heffer [1967] HCA 40; (1967) 116 CLR 344, 350.
In Penrice v Williams (1883) 23 Ch D 353, 356-357, Chitty J spoke of an order that is 'clearly not of a final character, and also when there is necessarily something to be done irrespective of what appears on the face of the order'. His Lordship was there explaining that in some cases an order may by its very nature need to be supplemented to give full effect to it, in which event liberty to apply is implied and need not be expressly reserved. See also Fritz v Hobson (1880) 14 Ch D 542, 561; Cristel v Cristel [1951] 2 KB 727, 731. A decree of specific performance in the limited form previously described nevertheless is a 'final' order for the purpose of appeal and otherwise, and so, at least as to issues litigated, cannot be discharged or varied under liberty to apply, notwithstanding that further decisions and orders may yet have to be made in working out its consequences. What cannot be done under the guise of 'working out' an order is to vary it. (598)