Nationality of extreme independent socialists' leader visiting school (8)
I believe the answer is:
scottish
'nationality' is the definition.
(I've seen this before)
'extreme independent socialists' leader visiting school' is the wordplay.
'extreme' becomes 'ott' (I've seen this in other clues).
'leader' suggests taking the first letters.
'visiting' means one lot of letters goes inside another.
'school' becomes 'sch'.
The initial letters of 'independent socialists' is 'is'.
'ott'+'is'='ottis'
'ottis' inserted inside 'sch' is 'SCOTTISH'.
'of' is the link.
(Other definitions for scottish that I've seen before include "from 18 [MORAY], say?" , "So stitch up to be like Angus or Jock" , "Costs hit this nationality badly" , "northern folk" , "tongue" .)