ACROSS
 6. BOA TRACE = BOAT RACE <row involving Oxbridge?>
 8. <twisting> TORQUE = "TALK"
10. <energetic person> DYNAMO = MONDAY*
11. (ONE + INEPT)* = EN POINTE <ballet technique>
12. SCAN[-t] = SCAN <to analyse>
14. <lawyer's endorsement> NOTARISING = (NOT ARISING)
16. RE PAIR = REPAIR <correct>
17. <area that's elevated> UPLAND = U + PLAN + D
18. <reinforces> BUTTRESSES = BUT TRESSES
20. <annual showcase> EXPO = _EX_ _PO_
21. (WITH ZERO)* = HOWITZER <cannon>
23. TENCH outside _R = TRENCH <ditch>
25. <device> WIDGET = W I'D GET
26. <it's annoying> IRRITANT = RR inside TITIAN*

 1. <terrible> POXY = [-e]POXY
 2. ←(.i)ES I ANNOY A M(a.)← = MAYONNAISE <condiment>
 3. <sad and lonely> BEREFT = F inside BERET
 4. <foil> STOP = ←POTS←
 5. <prissy> BUTTONED-UP = BUTT ONE + DUP
 7. (STARTING POINT)* = TRAINSPOTTING <{Irvine} Welsh novel>
 9. <return to office> REINSTATEMENT = REIN STATEMENT
13. U COP IA after CORN = CORNUCOPIA <abundance>
15. PROSE* I + TORY = REPOSITORY <archive>
19. <sally> SORTIE = "SORE TEA"
22. <greek character> ZETA = E_T_ inside ZA
24. <list {lean}> CANT <slang>