I remembered the information from a page on the RSPCA website and I researched it before I answered the question. The Wiki Says:
"Temperatures under about 10°C/50°F are dangerous to fancy varieties of goldfish, though commons and comets can be exposed to slightly lower temperatures without a problem."
Fancy varieties come under radically different rules as they are subtropical they should be kept at 16-22C. Comets and common pond goldies the ones people normally associate with have a much larger range of temperatures they can survive in.
Wow never knew that, you learn something everyday, thanks for the info