The Siskina  AC 210, per Lord Diplock:
A right to obtain an interlocutory injunction is not a cause of action. It cannot stand on its own. It is dependent upon there being a pre-existing cause of action against the defendant arising out of an invasion, actual or threatened by him, of a legal or equitable right of the plaintiff for the enforcement of which the defendant is amenable to the jurisdiction of the court. The right to obtain an interlocutory injunction is merely ancillary and incidental to the pre-existing cause of action. It is granted to preserve the status quo pending the ascertainment by the court of the rights of the parties and the grant to the plaintiff of the relief to which his cause of action entitles him, which may or may not include a final injunction.
Fourie v Le Roux  UKHL 1, per Lord Scott of Foscote:
I would agree that, without the issue of substantive proceedings or an undertaking to do so, the propriety of the grant of an interlocutory injunction would be difficult to defend. An interlocutory injunction, like any other interim order, is intended to be of temporary duration, dependent on the institution and progress of some proceedings for substantive relief. But it is not in dispute that in suitable circumstances a freezing order may be, and often is, granted and served on the respondent before substantive proceedings have been instituted. Such an order is not a nullity. It is of immediate effect. If proceedings for substantive relief are not instituted, the freezing order may lapse in accordance with its own terms or, on an application by the respondent, may be discharged. But none of this indicates that the court had no jurisdiction to make the order. No "activation" of the jurisdiction is needed.