PhONEday was a change to the telephone dialling plan in the United Kingdom on 16 April 1995. It changed geographic area codes and some telephone numbers. In most areas, a "1" was added to the dialling code after the initial zero. In Bristol, Leeds, Leicester, Nottingham and Sheffield, the area codes were replaced with new codes and the subscriber numbers gained an extra digit. The PhONEday changes also made provision for new ranges of subscriber numbers in those five cities. A £16m advertising campaign, and an eight-month period of parallel running during which old and new codes were active, preceded the change. PhONEday followed a change made in May 1990, when the old London area code 01 had been released from use, permitting all United Kingdom geographic numbers to begin with this prefix