In 18 71, certain days were designated in law as being days on which no financial transactions could take place. This was to give workers a few guaranteed days off a year so that they didn't get completely exhausted working in factories every day of the year. Now everyone is entitled by law to five point six weeks of paid holiday per year - but this may or may not include bank holidays. The shops tend to do quite well on a bank holiday week end, and so they stay open.