In the UK there is no law for minimum size cages for hamsters. Even though there's so much information out there. 

Hamster who are kept in smaller cages live a very stressful life, they are not able to express their natural behaviours, which according to the 5 welfares all animals should be able to express. 

Here in the UK 50x80cm is the very minimum recommended. 

I want all pet shops to only sell hamster cages that are the correct size. Anything less than this is animal abuse.