Son with HM in a grand rambling royal residence (11)
I believe the answer is:
sandringham
'royal residence' is the definition.
(I've seen this before)
'son with hm in a grand rambling' is the wordplay.
'son' becomes 's' (**).
'with' says to put letters next to each other.
'rambling' is an anagram indicator.
'hm'+'in'+'a'+'grand'='hminagrand'
'hminagrand' is an anagram of 'andringham'.
's'+'andringham'='SANDRINGHAM'
(Other definitions for sandringham that I've seen before include "Without adequate scrutiny" , "Queen's Christmas residence" , "Royal home" , "Royal residence in Norfolk" .)