One’s accompanying the Queen visiting military hospital and mess (8)
I believe the answer is:
mishmash
'mess' is the definition.
(I've seen this before)
'one's accompanying the queen visiting military hospital' is the wordplay.
'one's' becomes 'is' (Roman numeral).
'accompanying' says to put letters next to each other.
'the queen' becomes 'hm'.
'visiting' means one lot of letters goes inside another.
'military hospital' becomes 'mash' (abbreviation for mobile army surgical hospital).
'is'+'hm'='ishm'
'ishm' placed into 'mash' is 'MISHMASH'.
'and' is the link.
(Other definitions for mishmash that I've seen before include "mess" , "Jumble" , "Jumbled mix" , "Hotchpotch, melange" , "muddle?" .)