ACROSS
1. (PIANIST PALS SHIT)* = THIS IS SPINAL TAP <musical mockumentary>
9. ←CAMO TOP← = POTOMAC <one running in DC>
13. "NICK A SEER" = NICOSIA <capital>
14. CO ←BITING outside EV← I AS _ES_ = COGNITIVE BIASES <flawed assessments>
15. GENE + ROD DEN BERRY = GENE RODDENBERRY <space programme's creator>
16. <he said sesame> ALI BABA = A_ L_ I_ B_ A_ B_ A_
17. TURIN outside NS = TURNS IN <surrenders>
18. <get topside> REACH THE SURFACE = (AFTER + HER CACHES U_)*
19. (INDEED outside PEN DE N C) + A Y = INDEPENDENCE DAY <US celebration>
23. <stumbled across> HIT UPON = TU inside HIP O_N
25. <condemns> DECRIES = DRIES outside E_C
26. SORT YOU (SOFT RULE)* = SORT YOURSELF OUT <to get it together>
27. <city> SAINT PETERSBURG = (PARIS'S TENET)* + ←GRUB←
28. <old> ONE-TIME = (...t)O NET I ME(n...)
29. R ACHED outside _N_ = RANCHED <did farmwork> 
30. <Tyrone's here> NORTHERN IRELAND = NOR (THERE outside RN _I_) LAND
31. COUNT Y_ F_ + ⭯MANAGER⭯ H = COUNTY FERMANAGH <somewhere around 30 {NORTHERN IRELAND}>
36. GO + TEASE* = GOATEES <some hair>
39. POSTER, WA←E = POST-WAR <after armistice?>
40. HEAR TB RE AK EL outside HOT = HEARTBREAK HOTEL <Elvis single>
41. (...o)UNDERS ADD LEY OK E(t...) = UNDER SADDLE YOKE <somewhere high up in Dumfriesshire>
42. "HER SUIT" = HIRSUTE <rather hairy>
43. MEN inside DEED* = EMENDED <put things right>
44. X FRIDAY* FRACTION = X-RAY DIFFRACTION <evidence of crystalline structure>

DOWN
1. TIGHT outside ON = TONIGHT <this evening>
2. <opposed> IN CONTRADICTION = _INC_ ON TRADITION outside C
3. <gets cover for> INSURES = SUNRISE*
4. STAN DO NO (END HE'S A)* = STAND ON ONE'S HEAD <to see things another way?>
5. <unencrypted> IN CLEAR = I_ + N_CLEAR
6. A LG EASER outside BRA ICER = ALGEBRAIC ERASER <encryption protocol>
7. _T_R _I_A_R_ C_H = TRIARCH <one of the three people in charge>
8. PLUNGER outside I NYT HEY _O_ = PLINY THE YOUNGER <Roman lawyer>
9. P REF A + BS = PRE-FABS <cookie-cutter houses>
10. <explosive> TRINITROTOLUENE = TRINIT_ + ROT + ONE outside _LUE
11. <cosmetic> MASCARA = MA + SCA + R_ A_
12. <West Coast buckwest> CASCADE KNOTWEED = CA SNACKED* + O TWEE D_
19. <regulatory corruption> INDUSTRY CAPTURE = IN D (PAY STRUCTURE)*
20. <cut loose> PAINT THE TOWN RED = N inside (POET HAD WRITTEN)*
21. <type of Christian> EASTERN ORTHODOX = EASTER + NORTH O_ D_ O_ X
22. <be cheering> DO YOUR HEART GOOD = (DRY DAUGHTER)* outside O O OO
23. <past scholar> HISTORIOGRAPHER = (OR A HIGH PRIEST)* outside OR
24. PRO XI MACE + NT R_ I_ outside AU = PROXIMA CENTAURI <star>
32. <bear family> URSIDAE = ←(...t)EAD IS RU(d...)←
33. FORD outside WAR = FORWARD <at the Front>
34. <poplar-lined avenue> ALAMEDA = (À LA) MED _A_
35. <she reflexively> HERSELF = (HEARS - _A) + ELF
37. A M_H ←CIA← outside R = AMHARIC <the talk of Addis Ababa>
38. SN outside ALTER = SALTERN <seawater evaporation site>