No 11894, Tuesday 03 Jan 2017, Arden

I personally found it tough going today.

ACROSS
1   Money collected — a pound for the hood (6) CALASH {C{A}{L}ASH}

4   Choose to admit the boy, is he the one who is upbeat? (8) OPTIMIST {OP{TIM}{IS}T} 'He the' is misleading
10 Use a net around it to make a solid solution of Carbon in Iron (9) AUSTENITE {USE+A+NET}* around {IT}
11 Weak but runs without fail (5) FRAIL {F{R}AIL}
12 Boast about light form of anagram (7) GARBLED {BRAG<=}{LED}
13 Making noise about a large mammal (3,4) SEA LION {NOISE}* about {A}{L}

14 A doctor embracing another in dance (5) MAMBO {M{A}{MB}O}
15 Limited food, it doesn't amount to much (8) FARTHING {FARe}{THING}

18 High current — restricts current for rear light (4,4) TAIL LAMP {TA{I}L L}{AMP}

20 Block one with desire, it's said (5) ANVIL {AN}{VIL}(~will)
23 Sarah is making a paste of chilli, garlic and spices (7) HARISSA* Thanks to Google

25 Before returning money, cultivate this strip of land (7) ISTHMUS {THIS}*{SUM<=}
26 You're said to owe money in the beginning (5) DEBUT (~ ?? you) (Addendum - {BEB(U)T) - See comments)
27 Come between breaks — no respite... (9) INTERPOSE*
28 ...and Andrew lost one and backed out (8) WITHDREW {WITH}{anDREW}
29 Cruel of her to return on board the ship (6) OGRESS {ERGO<=}{SS} Something wrong in the wordplay. 'Of' is returning and not 'of her' (Addendum - {GO<=}{RE}{SS} - See comments)

DOWN
1   About to strike, match could be a gamble (4,4) CRAP GAME {C}{RAP} {GAME}
2   Long for a drink every five years (7) LUSTRUM {LUST}{RUM}
3   Brace down, it's abrasive (5,4) STEEL WOOL {STEEL} {WOOL}
5   Pen, perhaps for vulnerable locations (8,6) PRESSURE POINTS [DD] First half of definition not clear (Addendum - {P}{EN} - See comments)
6   In 50% of the country, it's found below (5) INFRA {IN}{FRAnce}
7   Sex with a pin up for a foreign national (7) ITALIAN {IT}{A}{NAIL<=}
8   Wine bottles — a litre as a gift (6) TALENT {T{A}{L}ENT}
9   Ear drop is bad if used for a flyer (4,2,8) BIRD OF PARADISE*

16 Squeeze out soil under river, place it before the fireplace (9) HEARTHRUG {H{EARTH}{R}UG}
17 Happiness over a short period forms bubbles (8) BLISTERS {BLIS{TERm}S}
19 One's after a thief breaking the law, and he tumbles (7) ACROBAT {AC{ROB}{A}T} Thief/Rob? See comments
21 Go low inside vessel (7) VAMOOSE {VA{MOO}SE}
22 Pig has had a double (6) SHADOW {S{HAD}OW}
24 Said to take time off — is contented (5) SATED StATED

GRID