Moira Stuart's turning up wearing long garment (4)
I believe the answer is:
sari
'long garment' is the definition.
(type of Asian garment)
'moira stuart's turning up wearing' is the wordplay.
'wearing' indicates the answer is hidden within the clue (the answer is covered by or 'wearing' the clue).
'turning up' shows that the letters should be reversed in order.
'iras' is hidden within 'moira stuart'.
'iras' reversed gives 'SARI'.
(Other definitions for sari that I've seen before include "Traditional Indian women's dress" , "Traditional dress of Indian women" , "Indian robe" , "South Asian garment (variant spelling)" , "Hindu woman's dress" .)