Skin infection cases spread around British island (7)
I believe the answer is:
scabies
'skin infection' is the definition.
(I've seen this before)
'cases spread around british island' is the wordplay.
'spread' indicates an anagram.
'around' is an insertion indicator.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'island' becomes 'i'.
'cases' with letters rearranged gives 'scaes'.
'b'+'i'='bi'
'scaes' placed around 'bi' is 'SCABIES'.
(Other definitions for scabies that I've seen before include "Contagious skin disease causing itching" , "rash complaint?" , "Contagious skin infection" , "Contagious skin disease that causes itching" , "Skin disease - "The Itch"" .)