R v Clarkson

 Ds watched X rape a woman and did nothing to stop him. However they did nothing to encourage the rape nor was there evidence to show that they intended to encourage the rape. They were convicted but CA quashed convictions on basis that intent and act of encouragement had to be proved (not mere presence). Of course there could be instances where mere presence was the purpose of the event (e.g. illegal prize fighting) and could be construed as encouragement. Not the case here.