What should we make of the dramatic appearance of the Leveller leader John Lilburne in Hatfield Level in 1651, at the height of a decade of anti-improvement riots? This unusual contact between central radicalism and rural unrest destabilises binaries between a zealous minority driving civil war conflict and indifferent provincial subjects. Fen projects instead expose the pluralism of political ideas in seventeenth-century England. These crown-led ventures polarised notions of justice and became entangled in the events and debates propelling the English civil wars. In Epworth Manor, commoners across the social spectrum asserted an inalienable ‘just right’ to wetland commons in the face of royal and republican coercion. The strength of customary politics extended far beyond the parish, becoming a powerful means to articulate opposition to improvement in conflicts that moved between wetlands and Westminster. Central governors ultimately struggled to exercise a monopoly over legitimacy or violence in Epworth, where collective action across almost a century repelled efforts to turn their commons into theatres of state power and national productivity.