Tesco Clubcard (commonly referred to as Clubcard) is a loyalty card for British supermarket chain Tesco. Clubcard system operates in the UK, Ireland, Czech Republic, Slovakia, Hungary, Poland and many other countries. As of 2017 it has more than 17 million users in the UK alone. in 1993, Terry Leahy asked tesco's marketing team to investigate the potential of loyalty cards. In the past Tesco has been running green shield stamps as a promotional tool that rewards people for visits and spending but has not gained any customer information. The initial team, led by Grant Harrison, examined programmes around the world and developed a proposal that showed that a loyalty card could be very effective. The main change since the days of green shield stamps has been the ability to track the behavior of individual customers cost-effective using a magnetic bar card. in 1994, Harrison attended a conference where Clive Humby of dunnhumby marketing company was speaking. Dunnhumby was already working with clients such as Cable & Wireless and BMW, and Harrison approached them to help with the loyalty card project. Successful experiences throughout 1994 led tesco's board of directors to ask Harrison and Humby to submit them to the board's annual strategy session.