Restrict interest about who is regularly meeting heads of British Intelligence (7)
I believe the answer is:
inhibit
'restrict interest' is the definition.
'inhibit' can be an answer for 'restrict' (inhibiting is a kind of restricting). I'm not sure about the 'interest' bit.
'about who is regularly meeting heads of british intelligence' is the wordplay.
'about' is an insertion indicator.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'meeting' is a charade indicator (letters next to each other).
'heads of' indicates taking the first letters.
'intelligence' becomes 'init' (I can't explain this - if you can you should give a lot more credence to this answer).
The first letter of 'british' is 'b'.
'who'+'is'='whois'
The alternate letters of 'whois' are 'hi'.
'hi'+'b'='hib'
'hib' put within 'init' is 'INHIBIT'.
Can you help me to learn more?
(Other definitions for inhibit that I've seen before include "Prevent expression of" , "Check - prevent" , "Hold back" , "Repress" , "Constrain" .)