U.K. pins are 4 digits, but many European countries, the Far East and Middle East/North Africa use 6 digit pins. I have found, that ‘foreign’ ATMs requiring 6 digit pins accept my U.K. card and a 4 digit pin and similarly U.K. ATMs will accept the first 4 digits of my European bank card.
I don’t know what bank I was using, but I was also able to use my six digit bank card in the UK this summer (to be honest, I don’t know if just used the first four digits or all six - I know I typed in all six but it may have stopped paying attention after four).