The Greater London Authority (Protected Information) Order 2000
Under section 61 of the Greater London Authority Act 1999, the London Assembly may require certain categories of person (including members of staff, members and officers of functional bodies, those to whom it has given financial assistance, the Mayor and its own members) to attend its proceedings for the purpose of giving evidence, or to produce documents. Such persons may refuse to do so if such information or document is within a category of information, or of documents, prescribed by the Secretary of State by order under section 63.