The Strategic Policy Statement (SPS) is a discretional policy tool, introduced under the Energy Act 2013, for use by a Secretary of State. There is no obligation for a Secretary of State to issue an SPS.
Under the Gas Act 1986 and the Electricity Act 1989 Ofgem’s principal legal duty is to protect the interests of existing and future consumers, including “their interests in the reduction of electricity (and gas) supply emissions of targeted greenhouse gases”. The regulator must also have regard to the gas and electricity systems’ effect on the environment (Part 1, section 5 of GA86 and EA89).
Ofgem is required to have regard to guidance issued by the Secretary of State on environmental and social matters when carrying out its duties and functions. Ofgem sets out annually how it is has helped the Government make progress towards its environmental goals. https://www.ofgem.gov.uk/publications-and-updates/letter-secretary-state-social-and-environmental-guidance-2018