Overwhelming Supervening Acts - All Theory, No Practice?

This is a case comment on R v Ayre [2025] EWCA Crim 255. In Ayre, the Court of Appeal (CA) dismissed appeals against convictions for manslaughter and related offences arising from a deliberate car attack following a confrontation. The appellants argued there was insufficient evidence of encouragement and that the driver’s actions constituted an ‘overwhelming supervening act’ (OSA), breaking the chain of liability. The court rejected this, holding that a secondary party need only intentionally assist or encourage the principal with the requisite intent; it was unnecessary to prove that such encouragement had had a positive effect. The appellants’ conduct (threatening the victims and joining the armed pursuit) remained contemporaneous encouragement and had not ‘faded’ into the background. My commentary criticises the decision for adopting an unduly narrow approach to OSA, rendering it rarely applicable once a shared intent to cause grievous bodily harm is established, even where the principal offender significantly escalates the violence. This raises concerns that OSA has become largely theoretical in practice, providing no or no meaningful constraint on (constructive) accessory liability.