Drink to mark change Liberal left brought in (3,7)
I believe the answer is:
tom collins
'drink' is the definition.
(Tom Collins is an example)
'to mark change liberal left brought in' is the wordplay.
'mark' becomes 'm'.
'change liberal' becomes 'colins' (I can't explain this - if you can you should give a lot more credence to this answer).
'left' becomes 'l' (common abbreviation).
'brought in' is an insertion indicator.
'colins' enclosing 'l' is 'collins'.
'to'+'m'+'collins'='TOM COLLINS'
Can you help me to learn more?
(Other definitions for tom collins that I've seen before include "Gin-based cocktail" , "Cocktail using gin" , "Long iced drink of gin, lemon juice and soda water" , "Gin makes this" .)