Solution to 22D has been deliberately left unsolved and is to be answered by a non-regular/novice commenter, with proper annotation. Those who have answered earlier in the week, please give others a chance.
Open for anyone to answer, if not solved by 1 PM.
ACROSS
1 Collapse following blast - loud, primarily powerful (4,2) FOLD UP {F}{LOUD*}{Po...l}
4 Artist of Cuba, in drunken stupor, left (8) SCULPTOR {C} in {STUPOR+L}*
10 Appeal to queen about monument (9) CHARMINAR {CHARM}{RANI<=}
12 Condition of sailor carried by vehicle to hospital (7) CATARRH {CA{TAR}R}{H}
13 Gets Mark to cycle after a time (7) ATTAINS {(-s)TAIN(+s)S}<=>{A}{T}
14 Rejected part of result as "Erroneous", attempted exam again (5) RESAT [T<=]
15 One who loves dogs and birds (8) FANTAILS {FAN}{TAILS}
20 English students leaving parasol in shade (5) UMBRA UMBRellA
23 Timid fellow gets scolding (7) FEARFUL {F}{EARFUL}
25 Close sale? (4,3) SEAL OFF {SALE}* [RA]
26 Catch drum (5) SNARE [DD]
27 Hitler, say, cordial about Germany (9) WARMONGER {WARM}{ON}{GER}
28 It provides insight from analysis of heredity (5,3) THIRD EYE*
29 Story about invading Spain - it could reveal something valuable (6) OYSTER {OYST{E}R*}
DOWN
1 Maybe King's rage to quash conservative nation in revolt (4,4) FACE CARD {FA{C}{RACE<=}D}
3 Mutineer punished by duke? Not fair (9) UNMERITED {MUTINEER}*{D}
5 I insure art, cars, refurbished trailers (7,7) CURTAIN RAISERS*
6 Easy part of this grid (5) LIGHT [DD]
7 Inconsequential test - eventually one is overwhelmed by opponent (7) TRIVIAL {tesT}{RIV{1}AL}
8 Apparel is hand-crafted, revealing taste (6) RELISH [T]
9 Expecting easy finals in Open Bridge Tournament, why I may fail (2,3,6,3) IN THE FAMILY WAY {opeN+b...gE+t...nT+WHY+I+MAY+FAIL}*
17 Picked up much more pretty traveller (8) WAYFARER (~way fairer)
19 Bread ready to be dipped in tea (7) CHAPATI {CHA{PAT}I}
22 Compensate for rotten place (6) ?F?S?T (Addendum - OFFSET {OFF}{SET} - See comments)
Reference List
Following = F, Cuba = C, Left = L, Good = G, Hospital = H, Time = T, Accountant = CA, English = E, Student = L, Fellow = F, Spain = E, Rage = FAD, Conservative = C, Duke = D, Active = A, Rupees = R