Case I mixed up, going round information bureaux (8)
I believe the answer is:
agencies
'bureaux' is the definition.
('agency' can be a synonym of 'bureau')
'case i mixed up going round information' is the wordplay.
'mixed up' indicates an anagram.
'going round' indicates putting letters inside (some letters go around others).
'information' becomes 'gen' (gen can informally mean information).
'case'+'i'='casei'
'casei' with letters rearranged gives 'acies'.
'acies' enclosing 'gen' is 'AGENCIES'.
(Other definitions for agencies that I've seen before include "Businesses that provide services on behalf of another businesses" , "Businesses that serves other businesses" , "Businesses that provide services on behalf of others" , "Businesses providing specific services" , "Firms who transact business for others, perhaps actors" .)