ACROSS
1. UK _E outside PTA = UPTAKE <level of participation>
4. V _A_ (B R inside MACE) = VAMBRACE <defensive piece>
10. <split> CLEFT = C_ LEFT
11. <French stew> CASSOULET = (LOST CAUSE)*
12. ALL outside MARBLE* = ALARM BELL <siren>
13. MO XI + E = MOXIE <fighting spirit>
14. PER SNICKET + _INESS_ = PERSNICKETINESS <attention to detail>
17. (THE SUN) ARISES outside LSO = THE SUN ALSO RISES <Hemingway novel>
19. <establish> FOUND = FUND outside O
21. <perseveres> PRESSES ON = RESPONSES*
23. <they're charged> ELECTRONS = ←SNORT + CELE_←
24. <studies> READS = "REEDS"
25. <crystal> AMETHYST = METH inside A ⭯STY⭯
26. (DRESDEN - S_)* = REDDEN <blush>

DOWN
1. <release> UNCLASP = ←PSA← under UN C_L
2. (THEE outside FA_) QUIRE* EEN E = THE FAERIE QUEENE <Spenserian epic>
3. _K AT H (MAN U) outside D = KATHMANDU <capital city>
5. <they'll forgive> ABSOLVES = AB SOLVERS
6. <thrive> BLOOM = L_ inside BOOM
7. <entirely complimentary> ALL-EXPENSES-PAID = (EXPLAINED LAPSES)*
8. <dishes> ENTREES = "ON TRAYS"
9. AC M_E = ACME <top of the range>
15. <defends> CHAMPIONS = A MP inside CHINOS*
16. (IN RE) SERVE = IN RESERVE <saved for later?>
17. ←FAT← FETA = TAFFETA <cloth>
18. S_ (INKS IN) = SINKS IN
20. D_ ITCH = DITCH <trench>
22. <facilitate> EASE = "E'S"