One with tension at the end of term? (8, first letter M) Can't see this one - thought it might be anagram of tension + m - but all that gives is 'mentions'?
The answer can only be one of two or three possibilities but I cannot see it. 21 a Become established in non-standard evenings after backing. (3,2) S-T, -N
A few I'm not quite sure about. 10A Supplementary to town in Lancashire (4-2) -O-T,-N 17A Interest in a post (5) S-T-E Clue of the week: Every second of every minute someone plants a flower (5)
15 d What Sweden exhibits literally, so to speak is generosity L-R-E-S- (8) I think it's Largesse, but cannot see why. Similarly, 21 d It's OK with old clothing on A-R-E- (6)...I think it's Agreed but...