[1] The card works on a point-based system, where holders receive points based on money spent.

In 1993, Terry Leahy asked the Tesco marketing team to investigate the potential of loyalty cards.

In the past Tesco had run Green Shield Stamps as a promotional tool which rewarded people for visits and spending, but gained no customer information.

The initial team researched programmes across the world and developed a proposal which showed that a loyalty card could be very effective.

The key change since the days of Green Shield Stamps was the ability to track individual customer behaviour cost-effectively using a magnetic stripe card.

Dunnhumby was already working with clients such as Cable & Wireless and BMW, and Harrison approached them to help with the loyalty card project.

The first response from the board came from Tesco's then-chairman Lord MacLaurin, who said, "What scares me about this is that you know more about my customers after three months than I know after 30 years.

"[3] In January 1995, Frank Riolfo, a former lance-corporal of the Royal Army Medical Corps, extorted Tesco, forcing the introduction of the previously trialled discount card.

After first contaminating food with (what turned out to be fake[4]) HIV-infected blood in a store in Kettering, Riolfo demanded payment via Tesco's new loyalty card system.

Riolfo and his wife then toured the country withdrawing a total of £7,500 cash on 73 occasions until they were eventually caught on 22 April 1995.

[6] In the end of 2000, Robert Edward Dyer made a similar attempt at extortion involving Clubcards with a magnetic strip for ATM withdrawals.

[9] Though operating in a similar fashion to the scheme in the United Kingdom, it is independent, so Clubcards from other countries cannot be used in Slovakian or Polish stores.

[20] Starting in the end of 2010,[21] Tesco launched applications for iPhone, BlackBerry, Android and Nokia Ovi, so points can be collected by presenting a barcode on the handset instead of a keyfob or card.