I worked steadily through this in very nearly 18 minutes, some of the time thinking there’d be struggles in some quarters, what with TLS qualified authors and non-Python philosophers, a bizarre plant or two, and bits from Latin and Greek. Feel free to rumble menacingly about the liberties taken by setters in feeding this habit of ours. On the other hand, there are some quite inventive devices in several clues to take us off the beaten track of solving, though one of them at 18 is, I think, a bit muffed.
I provide the clues in italics, the definitions therein also underlined, and the SOLUTIONS just so
ACROSS
1 Sees hint about locations where drivers may pull in (3,5)
PIT STOPS A generous reversal clue (about) in which sees hint becomes SPOTS TIP to provide the required letters
5 Prevent what allows youngster to fall asleep in school (6)
SCOTCH Those of us who have experience of the smaller variety of human might hope that a COT allows them to sleep. More like provides a space where, by some miracle, they might just stop their primary activities of creating noise and ordure if we’re very lucky. Anyway, place it in SCH(ool)
9 Period of time in which to embed a plant (8)
CENTAURY Nope, not in my garden. Or my vocab. But take a chance and embed A in CENTURY, which is a well enough known period of time.
10 Margaret with expression of surprise — maiden showing a lot of resistance (6)
MEGOHM The Margaret in my family was indeed a maiden aunt. We didn’t call her MEG, she might occasionally have expressed surprise with an OH, and we’d never have referred to her as a M(aiden) in her hearing, but the three elements still combine to make a significantly high measure of electrical resistance compared to a single ohm. A million times the size.
12 Studied English to become an author (5)
READE Probably Charles, who wrote The Cloister and the Hearth on the imagined life and adventures of the parents of Erasmus, and much besides. READ for studied with an E(nglish) tacked on.
13 Step up, being against standing still (9)
PROMOTION If you’re against standing still, you might be PRO MOTION.
14 Hurried down at first and fell (12)
PRECIPITATED Hurried gives the adjective PRECIPITATE, and if you put a D(own) on the end it becomes the past tense fell, as in rain.
18 Unwise financial procedure that could have company in money, strangely (5,7)
FALSE ECONOMY I rather think the clue works better without the anagram indicator “strangely”, which when applied to CO(mpany in) MONEY produces the ECONOMY. But I don’t really see where the FALSE comes from. Without “strangely”, it works as a rather nifty reverse cryptic clue in which the answer provides a clue to produce company in money, with “false” acting as the anagram indicator.
21 Report can supply just the opposite (3,6)
PER CONTRA Supply here is an anagram indicator, applied to REPORT CAN relatively easy Latin.
23 Falsetto’s cast in part in opera (5)
TOSCA Today’s “hidden” answer (in part) in FalsetTOS CAst. Just because I can, here is the Japanese male sopranist Tomotaka Okamoto singing (arguably in a fantastic falsetto) Ms Floria Tosca’s aria “vissi d’arte” from the Puccini opera.
24 Body of legislators had to back second measure (6)
SENATE Had as in ATE behind S(econd) EN, a measure in type
25 Dealing with famous author (8)
FIELDING Several candidates, not including the still-living Helen who is responsible for Bridget Jones’ Diary. Henry, maybe. I will be available for fielding questions on the subject at intervals in the day.
26 Shocking treatment you guards quietly copy (6)
ECTYPE Trust the cryptic time. ECT (Electro Convulsive Therapy, which I’m surprised to see is both current and approved treatment) plus YE for you “guarding” P for quite. A philosophical rather than an office machinery concept.
27 Go hunt, us? Quite otherwise, if something’s this (8)
UNSOUGHT Pretty much an &lit, in which the anagram (quite otherwise) of GO HUNT US produces a situation (our answer) in which go hunt us wouldn’t happen.
DOWN
1 Astronaut, first to last, nags (6)
PACERS Horses, that is, that kind of nags. An astronaut might be described as a SPACER, and you then move the S to the other end.
2 Secret society joined by a new islander (6)
TONGAN The secret society is the Chinese version TONG, plus A and N(ew)
3 Rather unpleasant fellow, say, always turning up (2,1,6)
TO A DEGREE Unpleasant fellow TOAD, say (for example) EG, plus E’ER for always turned up.
4 Shrewdness a star’s shown when joining urban community (12)
PERSPICACITY One of those where the innocuous A must be read as PER (two A penny). SPICA is the brightest star in Virgo, and the urban community is, unsurprisingly, CITY.
6 It’s right in church to perform part of service in Latin (5)
CREDO R(ight inserted into C(hurch of) E(ngland) and DO for perform added.
7 Philosophers? Most of that lot maybe fret inwardly (8)
THOMISTS Take most of THOS(e) and insert MIST for that sort of (sea) fret. Thomists are of the school of Thomas Aquinas.
8 Carriers conveying small ancestors of ours? (8)
HOMINIDS HODS are carriers (for bricks, but you knew that) and they “convey” MINI for small.
11 Companies not fussed about providing payment for injury? (12)
COMPENSATION An excellent anagram (fussed) of COMPANIES NOT.
15 Man has a dig to get round plant (9)
TOMATILLO Of the nightshade family producing berries much used in Mexican cuisine. I would say trust the cryptic again, but it’s not quite so easy. TOM is your random man, A is in plain sight, TILL stands in for dig, and you then get a round O. Hm.
16 It could suggest I step where one may slither dangerously? (3-5)
OFF-PISTE Another (this time definitely) reverse cryptic clue, in which the answer is a clue to I step, being an anagram (OFF) of PISTE. I toyed with ice-space and similar for a while as homophonic, almost.
17 Music-maker having wine outside home (8)
CLARINET Pleasant wine, CLARET, outside IN for home.
19 Regal request? (6)
ASKING In which regal is (behaving) AS KING
20 Plasterwork that is what you expect to obtain (6)
PARGET Commonplace round these parts, decorative plaster applied to the outside of houses to make them look pretty. Aficionados my recognise the Pargetter family from The Archers whose name derives from the craft. What you expect is PAR (for the course) and obtain provides the GET
22 Indication of what’s hot or cold may be here, readily available (2,3)
ON TAP “A cryptic hint plus a definition”. Just to prove I do read the contributions.
27’11” all green
COD PROMOTION
TIME 20:10 in vain
Thank you, z8b8d8k and the setter
Lots of complaints about it being hard, but the snitch is only just over 100. I think perhaps it favoured the old guard somewhat, who might be more used to solving clues where the answer is obscure
I’d be quite interested to know what prompted your comment. Some deep personal unhappiness, perhaps?