Trail behind Her Majesty getting a drink (5)
I believe the answer is:
lager
'a drink' is the definition.
(lager is a kind of drink)
'trail behind her majesty' is the wordplay.
'trail' becomes 'lag' (both can mean to go behind).
'behind' says to put letters next to each other.
'her majesty' becomes 'ER' (Elizabeth Regina).
'lag'+'er'='LAGER'
'getting' is the link.
(Other definitions for lager that I've seen before include "Bottom-fermented beer" , "Light beer; sounds like camp" , "A brew" , "African camp" , "drink in the bar?" .)