UK farmers are facing significant uncertainty due to recent post-Brexit policy changes. Upland farmers in England are particularly at risk, due to their high dependence on European subsidy support payments. Farm entrepreneurship strategies may be a viable solution for these farmers to achieve economic sustainability while continuing to make valuable social and environmental contributions via multifunctional enterprises. However, many socio-economic constraints often prevent farmers from implementing these strategies. This paper builds upon existing research on ‘constrained entrepreneurship in UK agriculture’ by examining the Constrained Institutional Contexts that upland farmers operate within. Using a qualitative approach, the paper explores and theorizes how upland farmers are constrained by exogeneous forces which control access to and dependence on resources. The findings highlight the importance of a supportive rural environment for farm entrepreneurship; however, they also reveal that the success of such strategies is often beyond the control of individual farmers and policy support is often necessary to alleviate these constraints.