The audience in the United Kingdom originally listened to their radio sets by permission of a wireless license issued by the British General Post Office (GPO). However, under terms of that wireless licence, it was an offence under the Wireless Telegraphy Act to listen to unauthorised broadcasts, which possibly included those transmitted by Radio Luxembourg. Therefore, as far as the British authorities were concerned, Radio Luxembourg was a "pirate radio station" and British listeners to the station were breaking the law (although as the term 'unauthorised' was never properly defined it was somewhat of a legal grey area).