Source: pp 51-52, The Rule of Law (2010) by Thomas Bingham
But some exercises of judicial power are usually described as discretionary.
For example, while some remedies, notably damages, may be claimed as of right if liability and resulting damage are proved against a defendant,
others, notably an injunction, are discretionary in the sense that the judge is not bound to grant an injunction even if liability is proved. He has a discretion whether to grant one or not. But rules have grown up to direct the exercise of this discretion.
If the defendant’s conduct is shown to be unlawful,
and to be likely to cause harm to the claimant for which he will not be adequately compensated by damages,
and if the defendant appears likely to go on doing whatever it is that the claimant complains of and gives no undertaking to desist,
the judge is virtually bound to grant an injunction restraining the defendant from acting in that way. He has a discretion, but it is a discretion in name only because it can only be exercised one way.
I do not understand the bold; why can the judge's discretion be exercised only one way? Discretion can imply granting or refusing a request for an injunction?