Teen regrets bad time in London thoroughfare (6,6)
I believe the answer is:
regent street
'london thoroughfare' is the definition.
(I've seen this before)
'teen regrets bad time' is the wordplay.
'bad' is an anagram indicator.
'time' becomes 't'.
'teen'+'regrets'='teenregrets'
'teenregrets' is an anagram of 'regentstree'.
'regentstree'+'t'='REGENT STREET'
'in' is the link.
(Other definitions for regent street that I've seen before include "Central London thoroughfare" , "London shopping area" , "London shopping thoroughfare" .)