If you smear them on a white paper towel it will stain black or dark blood red. Your description sounds like mite.
They are a terrible thing and can kill a snake. They also spread like a plague.
Be aggressive in this battle.
Not sure if this product is available in the U.K. Maybe some U.K. members can suggest something else.
http://www.thamnophis.com/forum/husbandry/9493-provent-mite-usage.html