Drop of tea, we hear, in blue vessel (8)
I believe the answer is:
Here is my best explanation:
'drop of tea' is the definition.
'downturn' can be an answer for 'drop' (I've seen this before). I'm unsure of the 'of tea' bit.
'we hear in blue vessel' is the wordplay.
'we hear' becomes 't' (I can't justify this - if you can you should give a lot more credence to this answer).
'in' means one lot of letters goes inside another.
'blue' becomes 'down' (I've seen this before).
'vessel' becomes 'urn' (urn is a kind of vessel).
't' put inside 'downurn' is 'downturn'.
(Other definitions for downturn that I've seen before include "Deterioration", "Drop", "(Economic) decline", "Worsening of economic activity", "A worsening of economic activity", "Reduction in business", "Decline eg of economic activity" and "Decline in business".)