The Arc will be a hotspot for development over the coming 30 years, but will also require significant amounts of environmental offsetting to mitigate the impact of this development, creating new opportunities for landowners. As expected the Environment Bill 2019, published in October, formally introduces the concept of Net Environmental Gain on all development. In essence, net gain means that the environmental impact of a development is quantified prior to planning being granted. This impact is calculated in biodiversity units. The emphasis will be on avoiding impact in the development, and then mitigating within the master planning of the site.

However, in many cases a surplus of units will be needed to deliver the required 10% improvement, so an agreement will be needed with a landowner near the site to implement an environmental management plan that delivers the necessary biodiversity gain over a 25–30 year period. Net Environment Gain is not intended to enable development on protected or irreplaceable habitats, but to take an additional slice out of landowners’ planning gain to improve a habitat nearby that merits investment.

Urban land currently accounts for 9% of land use in the corridor. Savills estimates that building 1 million new homes will require almost 35,000 hectares of new urban land, increasing the total urban land cover to 12%. An average Net Gain scheme on farmland yields around four biodiversity units per hectare at an average value of £9–15,000 per unit for the duration of the management agreement. However, the number of hectares required for offsetting will depend on the ability to limit the overall environmental impact of development, and to mitigate onsite to start with.

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