Is that true?
The fraud dept. of Tesco have blocked my card several times, when the transactions were normal. For example, I was purchasing wood from a company I'd used several times previously,.. and another time the card was blocked because I transferred money to a gambling site... again I'd previously transferred money to the same site on other occasions, over a period of several months, so it doesn't make sense why they'd have blocked the card on a particular random occasion, the amount was 50 Euro. They also claimed to have tried to ring me to confirm but that doesn't seem to have been the case.