Up street Trish designed garments (1-6)
I believe the answer is:
t-shirts
'garments' is the definition.
(T-shirt is an example)
'up street trish designed' is the wordplay.
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'street' becomes 'st' (abbreviation).
'designed' indicates an anagram (designed with the letters).
'st' in reverse letter order is 'ts'.
'trish' is an anagram of 'hirts'.
'ts'+'hirts'='T-SHIRTS'
(Other definitions for t-shirts that I've seen before include "Casual, collarless tops" , "Thirsts (anag)" , "Casual garments" , "Close-fitting casual tops" , "Leisure tops" .)