Originally Posted by
Points Scrounger
All I can think of would be that the rare U K "disabled" cards have only signature, no PIN at all in their CVM. The waiter's POS was programmed to ask for a PIN if that option appeared anywhere on the card's list, detecting your (underlying) one.
Maybe there was a communications failure and only offline transactions worked? We don't know what an online-only signature card would have done though.