It is mandatory for quoted companies, large unquoted organisations and large limited liability partnerships (LLPs) to disclose environmental performance information through company filings. “Large businesses” are defined as companies exceeding two or more of the following criteria within a financial year; 250+ employees; an annual turnover of £36m, or an annual balance sheet total of £18m.
At a minimum, large unquoted companies and LLPs will be required to report on UK energy use and emissions from gas, electricity, and transport. Unquoted companies must publish global GHG emissions from activities for which the company is responsible and global energy use.
For all three organisation types, figures must be provided the previous year (if applicable), along with at least one intensity ratio or normalisation factor (e.g. CO2e / m2 of floorspace, or per employee), as well as a narrative around measures taken for emission reduction and details of the methodology used.
Source: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/850130/Env-reporting-guidance_inc_SECR_31March.pdf