SANGS can be taken into account by local authorities considering development proposals, but they must be real and deliverable, not hypothetical.
Much of the pressure on the planning system at present stems from the drive to increase delivery of new housing, particularly in the face of the housing delivery test coming into force in November 2017 pursuant to the Housing White Paper. It is inevitable that there will be increasing tensions between this aspect of the regime and other policies intended to protect both the natural environment and the built environment from overdevelopment.
Development versus protection
This tension is heightened in relation to development near land which is classified as greenbelt, greenfield land, areas of outstanding natural beauty and national parks. Some green spaces are afforded greater protection than others; particularly those designated as European sites or European offshore marine sites, which includes areas designated as Special Protection Areas, Special Areas of Conservation, and Ramsar wetlands sites ('protected sites').
These benefit from the protective measures contained in the Conservation of Habitats and Species Regulations 2010 (the 'Regulations'). Under the Regulations, the local planning authority ('LPA') must consider whether development proposals (alone or in combination) in the proximity of a protected site are likely to have a significant detrimental effect on it. If so, they should refuse consent, although mitigation measures can be taken into account (R (Hart DC) v. Secretary of State  2P&CR 16, para 76) including the provision of Suitable Alternative Natural Green Space ('SANGS').
Providing an alternative
If SANGS is offered, it must be real and deliverable, not hypothetical (R (Helford Village Company) v Kerrier DC  EWHC400 (Admin) paras 39, 40) and if financial contributions are to be made in lieu of contributing land for SANGS, they must be applied to some definite and achievable effective mitigation measures – simply making payments is not enough (Wealden DC v SoS DCLG  EWCA Civ 39, paras 30-34). This means that developers who propose to build in the vicinity of a protected site must not only find space for the development itself, including any affordable housing component, but also find space for SANGS. If pooled contributions are collected through CIL for smaller sites, for example, then the LPA must find the land and demonstrate that it is effective and deliverable as mitigation.
The idea of SANGS is not to replicate a protected site, but to provide easily accessible green space for every-day activities such as dogwalking, early morning runs, children playing on the way home from school, and a summer evening stroll. In other words, it is designed to take the pressure of 'ordinary' visits away from the protected site.