Offences Against Public Tranquillity
(1) An assembly of 5+ people is "unlawful" if their common object is: overawing the government/legislature/a public servant by criminal force; resisting execution of law/legal process; committing mischief/criminal trespass/other offence; forcibly taking/depriving property or rights; or forcibly compelling someone to do/not do something they're not legally bound to. (2)-(9) Membership is punished with up to 6 months' imprisonment, fine, or both - rising to 2 years for continuing after a lawful dispersal order, or for being armed with a deadly weapon; hiring, harbouring, or being hired for such an assembly carries comparable penalties.
This defines the foundational "unlawful assembly" concept underlying group-based public-order offences, and comprehensively criminalises every stage of involvement - joining, continuing, hiring others, harbouring participants, or merely offering to join - with escalated penalties for being armed or defying a dispersal order.
Five or more people gathering with the shared goal of forcibly resisting a lawful eviction order already constitutes an unlawful assembly under this section, even before any actual violence occurs.