Across: 1 SPIDERMAN + 1st letters (initially) of (D)ismisses (U)mpteen (O)fficial (O)bjections anagrammed (after adjusting = MODUS OPERANDI (his way of working), 8 Astray (OFf COURSE) minus one f (one fellow goes) = OF COURSE (predictably), 9 Take a look (PEER) reversed (around) inside the outer letters (outskirts) of (C)aerphill(Y) = (it’s) CREEPY (horrible), 10 MINIONS + CARDITIS anagrammed (struggling) minus 1st letter (losing primarily) of smell = DISCRIMINATION (taste), 13 Mum (PARENT) as dbe (for one) after (joins) pAPa minus outer letters (naked) = APPARENT (pretty obvious), 14 Alcoholic drinks (ALES) containing outer letters (peel) of P(lump)P = APPLES (fruits), 16 Wind instrument (FAN) inserted into (used during) current (IN) + T (opening of theatre) = INFANT (early), 17 Reversal (returning) of students (NUS) + BED (from the clue) containing (eating) middle letters (essentially) of cAKe = SUNBAKED (that’s bone dry and hard), 18 Expectation (HOPE) follows terrific (GREAT) + wine (WHITE) = GREAT WHITE HOPE (historically one people wanted to succeed), 19 Shout (CRY) + an alert that there’s something on the back (PTO) = CRYPTO (suggestive of hidden beliefs, eg Crypto-Judaism), 21 Thatch (as a verb, REED) containing (covering) popular (IN) + homophone (as told) of pub (IN)n = REINED IN (checked), 23 Accommodate (HOME) + writing desk (SECRETARY) = HOME SECRETARY (Office manager – manages the Home Office)  . 

Down: 1 Male (MAN) with seabird (PUFFIN) circling round (1st letter to last) inside = MUFFIN PAN (That’s handy for cooking), 2 Reversal (about) of prOUD without (forgoing) publicity (pr) = DUO (couple), 3 CD of SERVICE STATIONS (resting places), 4 Reversal (climbing) of police (CID) inserted into popular (indicating the commonly used name) food outlet (PRET) = PREDICT (forecast), 5 Asian perhaps (dbe of RACE) + opposing (AGAINST) + call to close pub (TIME) = RACE AGAINST TIME (pressurised situation), 6 Homophone (to say) of no (nay) = NEE (born), 7 Reversal (on reflection) of refusal of loan repayment cover (NO PPI) = IPPON (a winning move), 11 Whimsical reading (looks like) of CHAR+ADE  as fizzy tea = CHARADE (an absurdity), 12 Brat (IMP) on top of (placed on) every (EACH) = IMPEACH (charge), 15 Travel (PLY) containing (over) on the assumption that (IF) preceded by (carrying) old (EX) + (E)nglish) + (M)oney = EXEMPLIFY (show), 17 Hidden word (to some extent) = (unveiling) SPHERIC (of a ball), 18 Delivery (bIRTH) subbing G for B (using originally girl instead of boy) for the 1st letter (to open) = GIRTH (it shows how thick someone is), 20 Sock (MOP) reversed (over) = POM (Brit in Darwin), 22 Insert (during) (R)un into half of EAch = ERA (period).