Very keen not to allow into the Australian port (6)
I believe the answer is:
hobart
'port' is the definition.
(I've seen this before)
'very keen not to allow into the australian' is the wordplay.
I cannot really see how this works, but
'not' could be 'o' (I've seen this in other clues) and 'o' is located in the answer.
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is found in the answer.
'australian' could be 'a' and 'a' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for hobart that I've seen before include "Australian city" , "Tasmania's capital" , "Capital city of Tasmania" , "Capital city of 11 Across" , "Tasmanian city" .)