To explore the feasibility of meeting recently proposed large-scale tree planting targets, a UK wide assessment of land available for afforestation was carried out, considering a range of physical, environmental and policy constraints in three hypothetical planting scenarios. Results show there is sufficient space to meet these targets in all three scenarios, even if planting is prevented on good to moderate quality agricultural land and within protected areas. However, this would require planting on a large proportion of unconstrained land, especially for the more ambitious targets, which is unevenly distributed across the UK. This would limit opportunities for spatially targeting woodland creation, which may restrict the provision of additional ecosystem services such as air pollution control and recreation, and induce widespread negative impacts on landscapes and communities. In order to overcome these limitations, relaxing constraints, such as permitting afforestation of higher quality agricultural land, will need to be considered. Meeting many of the proposed afforestation targets would result in a transformational change in British land cover, which could replace or significantly impact the business models of tens of thousands of farms, and see the replacement of hundreds of thousands to millions of hectares of grassland, arable and horticultural land and other land covers. This would require rates of planting that far exceed those seen historically. Policies and mechanisms that could be used to encourage this planting, both by the state and private sectors, are discussed.