Enormous honour presented by Home Counties (5)
I believe the answer is:
obese
'enormous' is the definition.
(I've seen this before)
'honour presented by home counties' is the wordplay.
'honour' becomes 'obe' (Order of the British Empire award).
'presented by' means one lot of letters go next to another.
'home counties' becomes 'se' (Home Counties in the South East of England).
'obe'+'se'='OBESE'
(Other definitions for obese that I've seen before include "Enormously portly" , "getting well-upholstered" , "round" , "Falstaffian" , "Clinically overweight" .)