ISI is formally approved by the Secretary of State for Education to inspect independent schools in England, which are members of associations affiliated to the Independent Schools Council.
The Secretary of State’s power to approve inspectorates is regulated by statute and delegated legislation. The key provisions are in the Education and Skills Act 2008 (section 106).
The Secretary of State has a parallel power in relation to the inspection of boarding care in schools in the Children Act 1989 (section 87A).
Advice from the Department for Education sets out detailed expectations of inspectorates which must be met for continued approval.
The Secretary of State’s approval of ISI is set out in a formal letter and agreement:
Under ministerial direction, ISI and Ofsted also have a joint working arrangement based around the exchange of knowledge and understanding, with a view to informing best practice in each organisation.
This results in an annual report by Ofsted to the Secretary of State for Education.
The latest report can be found here.