Control apparatus (30), systems and methods for enabling access to one or more information systems (36) by one or more entities (34) on a path across a supply network to be controlled, access to the or each information system (36) being policed by means of an access-policer (38), the network comprising: at least one token-issuer (32) operable to issue an access pre-authorisation token, the access pre-authorisation token having associated therewith an information identifier and a digital signature, and to forward the access pre-authorisation token towards one or more entities (34) on a path across the network; and at least one receiver entity (34) operable to receive an access pre-authorisation token issued by the at least one token-issuer (32).