There is an advisory body called ACAI (Association of Consultant Approved Inspectors) and NHBC Building Control Services is listed as one of their members. ACAI website is
www.acai.org.uk/ and it says ‘Approved Inspectors are bound by the Code of Conduct of their own professional body and that of Construction Industry Council. ACAI Members are further bound by the ACAI Code of Conduct which includes a complaints procedure, providing further safeguards for the Client, and the assurance of best service from our Members.’