 Assault requires a positive act , not an omission . Mere lawful presence in a location is not enough to satisfy the conduct requirement ; illegal trespass , however , is sufficient . John Cyril Smith has suggested that wilfully refusing to retract an inadvertent act that causes the victim to apprehend violence may constitute an assault by omission . It is arguable that there was once a rule that " mere words " could not constitute an assault , but the case of R v Ireland confirmed that even silent phone calls would be grounds for the charge of assault . R. v Constanza added threatening letters to this category . 
