Phone spy about British head of intelligence (6)
I believe the answer is:
mobile
'phone' is the definition.
(I've seen this before)
'spy about british head of intelligence' is the wordplay.
'spy' becomes 'mole' (I've seen this before).
'about' means one lot of letters goes inside another.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'head of' suggests taking the first letters.
The first letter of 'intelligence' is 'i'.
'b'+'i'='bi'
'mole' going around 'bi' is 'MOBILE'.
(Other definitions for mobile that I've seen before include "Able to get around" , "Able to move or be moved easily" , "American port" , "Able to move about like modern phone" , "For European this is a handy" .)