I have answers but they puzzle me...
Across
12 Act that involves taking off top of skimpy outfit (4) S-I-
T= T shirt?
13 Anti-5? No, a variant (anti-17, say) (8) -O-A-I-N
I get the anagram, but not the rest. Is this one of the eight?
22 Original soul state (5,1) -R-A-X (X = slight guess)
As in Newsnight's Mark? And the ----- Soul Orchestra, but how does X (pres.) = state?
Down
21 Rupture of Ireland in olden times, but not in the same place (6) -E-N-A
anag of erin? but what's HA?
23 Amino acid in case where one end of nexus replaces the other (6)X-L-N-
presumably N swops to S or vice versa - I thought it was xylene but xylese doesn't mean anything (I'm useless at science, never having been taught much of it, so haven't a clue)