It's an awful line - was that "in Hyde Park?" (6,3)
I believe the answer is:
rotten row
'that in hyde park?' is the definition.
I know nothing about this answer so I can't judge whether this works.
'it's an awful line' is the wordplay.
'it's an awful' becomes 'rotten'.
'line' becomes 'row' (a row or line of things).
'rotten'+'row'='ROTTEN ROW'
'was' is the link.
Can you help me to learn more?
(Other definitions for rotten row that I've seen before include "Capital place for riding" , "Bridleway in Hyde Park" , "comes to an end at Hyde Park Corner" , "making foul noise?" , "Horses here" .)