The Scottish leader is given access by the guard (6)
I believe the answer is:
sentry
'the guard' is the definition.
(sentry is a kind of guard)
'the scottish leader is given access' is the wordplay.
'leader' indicates taking the first letters.
'is given' means one lot of letters go next to another.
'access' becomes 'entry' (entry is a kind of access).
The initial letter of 'scottish' is 's'.
's'+'entry'='SENTRY'
'by' is the link.
(Other definitions for sentry that I've seen before include "One who stands guard" , "Military guard" , "Watchman" , "Lookout person" , "Sentinel, look-out" .)