They have an investigatory arm of their own and have been known to go after corporate data, particularly email, as part of looking into what they believe may be

They have an investigatory arm of their own and have been known to go after corporate data, particularly email, as part of looking into what they believe may be tax fraud. One could reasonably question why this isn't a department or division of another agency, perhaps NCA, but I think it's a fair statement that forensic accounting and investigation is a somewhat specialised skill.