Hedgehogs are totally Nocturnal and should be regarded as ill if seen out in the day. Usually due to infection, disturbance , lack of food or water and hypothermia (sunbathing). These should be collected and put on a blanket covered hot water bottle in a cardboard box and offered clean water and food (wet cat food or Mealworms) . Please contact the British Hedgehog Preservation Society (BHPS) on 01584 890 801. 
The only exception to this is seen here when a nesting mother leaves her Hoglets in search of extra nutrition when her milk reserves can start to run dry.  ( Pictures mid June 2013) .