I had to write a big article thing on this at college. If I remember rightly the law is something like small shops can open all day (under 3000 square feet or something like that) large shops are restricted to six hours of business between the hours of 1000 to 1800.
But anywhere that is providing a "Service" are allowed to open all day no matter how big they are, Im not entirely sure how they define the word service but its places like hairdressers, service stations, pharmacies, restaraunts etc.