The Privacy and Electronic Communications (EC Directive) Regulations 2003

Use of electronic mail for direct marketing purposes where the identity or address of the sender is concealed

23.  A person shall neither transmit, nor instigate the transmission of, a communication for the purposes of direct marketing by means of electronic mail—

(a)where the identity of the person on whose behalf the communication has been sent has been disguised or concealed; or

(b)where a valid address to which the recipient of the communication may send a request that such communications cease has not been provided.