English: Mercury was formed in 1981 by Cable & Wireless to challenge British Telecom's monopoly. In 1986 street telephone kiosks were introduced in a variety of post-modernist styles, and with them, some very colourful telephone cards. These were especially useful as there was no minimum charge and a brief call could cost a few pennies. By the mid 1990s, these were already history. I guess this plaque dates from the early 90s BT Phonecards , much somewhat flimsier than the Mercury variant have also bitten the dust.