In R v Ireland  3 WLR 534 the appellant had been convicted of three counts of assault causing actual bodily harm under the Offences against the Person Act 1861.
Lord Steyn recounted the allegations and proceedings prior to the appeal to the House of Lords (now UK Supreme Court):
The case against [the appellant] was that during a period of three months in 1994 covered by the indictment he harassed three women by making repeated telephone calls to them during which he [would] remain silent. Sometimes, he resorted to heavy breathing. The calls were mostly made at night. The case against him, which was accepted by the judge and the Court of Appeal, was that he caused his victim to suffer psychiatric illness. [The appellant] had a substantial record of making offensive telephone calls to women. The judge sentenced him to a total of three years imprisonment.
An assault can be the unlawful application of force against a person (a battery) or through the unlawful intention to create apprehension of the immediate application of force: Fagan v. Metropolitan Police Commissioner  1 QB 439. The Court knew it was not the former, but could it be the latter?
Lord Steyn (Lords Goff, Hutton and Slynn agreed, Lord Hope penned his own judgment also agreeing),
That brings me to the critical question whether a silent caller may be guilty of an assault. The answer to this question seems to me to be "yes, depending on the facts." It involves questions of fact within the province of the jury. After all, there is no reason why a telephone caller who says to a woman in a menacing way "I will be at your door in a minute or two" may not be guilty of an assault if he causes his victim to apprehend immediate personal violence. Take now the case of the silent caller. He intends by his silence to cause fear and he is so understood. The victim is assailed by uncertainty about his intentions. Fear may dominate her emotions, and it may be the fear that the caller's arrival at her door may be imminent. She may fear the possibility of immediate personal violence. As a matter of law the caller may be guilty of an assault: whether he is or not will depend on the circumstance and in particular on the impact of the caller's potentially menacing call or calls on the victim. Such a prosecution case under [the relevant section] may be fit to leave to the jury. And a trial judge may, depending on the circumstances, put a common sense consideration before jury, namely what, if not the possibility of imminent personal violence, was the victim terrified about? I conclude that an assault may be committed in the particular factual circumstances which I have envisaged. For this reason I reject the submission that as a matter of law a silent telephone caller cannot ever be guilty of an offence under [the relevant section].
In Australia offences under 474.17 of the Commonwealth Criminal Code would probably have been charged, avoiding the issue.