 The Act created the offence of unlawfully intercepting communications sent by post or by a "public telecommunications system"; those guilty were liable, on conviction, to a fine or up to two years imprisonment.It provided for a system of warrants to permit legal interception, and laid down cases where interception could be done lawfully, stating that having reasonable grounds to believe that the other party consented to interception was a defence.The Act also established a complaints tribunal (which in 2000 was subsumed into the Investigatory Powers Tribunal), and created the post of Interception of Communications Commissioner to review the workings of the Act.