Accept something for tea to be the most remarkable thing (4,3,7)
I believe the answer is:
take the biscuit
'most remarkable thing' is the definition.
I don't know anything about this answer so I can't tell whether this works.
'accept something for tea to be the' is the wordplay.
'accept' becomes 'take' (to accept is to take possession of).
'something for tea' becomes 'biscuit' (I am not sure about this - if you are sure you should believe this answer much more).
'to' says to put letters next to each other (I've seen this in other clues).
'biscuit' put after 'the' is 'thebiscuit'.
'take'+'thebiscuit'='TAKE THE BISCUIT'
Can you help me to learn more?
(Other definitions for take the biscuit that I've seen before include "produce a big surprise" , "Grasp the cracker" , "Surpass everything else" , "surpass all the rest" , "beat everything - with 19d" .)