Starts talking freely in drink with old writer (5,2)
I believe the answer is:
opens up
'starts talking' is the definition.
(I've seen this in another clue)
'freely in drink with old writer' is the wordplay.
I cannot really understand how this works, but
'drink' could be 'sup' (to sup is to drink) and 'sup' is present in the answer.
'old' could be 'o' (abbreviation as in OT - Old Testament) and 'o' is located in the answer.
'writer' could be 'pen' (something which writes) and 'pen' is located in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for opens up that I've seen before include "talks without inhibitions" , "talks freely" , "starts shooting" , "Becomes more communicative" .)