Across:
1 Anchor (HOST-) found close to shore (close to 'shorE' = -E-) near port (port/left = -L) (HOSTEL), a stopover for backpackers (HOSTEL),
4 Picked up (MASTERED) by 19 down (‘master’ = MASTER-) working on paper (editor = -ED) (MASTERED),
9 Won’t find it in train set (‘it’ missing from ‘train set’ = ranset = ASTERN) or at the back of the ship (ASTERN),
10 Of course, warnings from those doing driving (‘fores’ = warnings on golf course = FORES-) test (-TRY) (FORESTRY) studying the layout of Barna Woods, for example (FORESTRY),
12 Wild (= anagram indicator) pure petal (pure petal = PERPETUAL) that’s everlasting (PERPETUAL),
13 Proportion of the taxable earnings going to church (TITHE) in Serengeti theocracy (in ‘serengeTI THEocracy’ = TITHE),
14 A fair amount of (half of) 18 across (half of ‘MASTERstroke’ = MASTER-) coming from the bakery (-PIE-) with limitless (i) frozen desserts (‘ices’ without ‘i’ = -CES) (MASTERPIECES) could be works of art (MASTERPIECES),
18 A touch of genius (MASTERSTROKE) from Mark (M-) – a relative of Daisy (-ASTER-) Butterfly, for one (butterfly STROKE) (MASTERSTROKE),
21 Cover story (ALIBI) of some Bengali bi-monthly (some ‘bengALI BI-monthly’ = ALIBI),
22 Didn’t hide the gossip (ANNOUNCED) from doctor (= anagram indicator), nun, deacon (nun deacon = ANNOUNCED),
24 To see the world (travel) mostly (l) (‘travel’ without ‘l’ = TRAVE-) with a sore eye (-STY) (TRAVESTY) is a poor substitute for the real thing (TRAVESTY),
25 A struggle (BATTLE) opening bottle (opening ‘Bottle’ = B-) for teetotaller (-TT-) surrounded by drink (ale = -A-LE) (BATTLE),
26 Arrests (arrests = REASS-RT) criminal (= anagram indicator) outside Spain (-E-) (REASSERT) for State again (state again = REASSERT),
27 Roman magistrate (CENSOR) buried up (= reverse indicator) in Rio de Janeiro’s necropolis (in ‘rio de janeiROS NECropolis’ = rosnec = CENSOR).
Down:
1 Warm up (HEAT) on the bicycle (PUMP) (HEAT PUMP) – it's bound to raise the temperature (HEAT PUMP),
2 Send up (SATIRISE) to satisfy (sate) nearly all (e) (‘sate’ without ‘e’ = SAT-) in upper (‘In’ upper = -I-) stand (-RISE) (SATIRISE),
3 Look (EY-E) over rental income tips (‘Rental Income’ tips = -RI-) (EYRIE) that might appeal to high flyers (EYRIE),
5 American (A) idiots (fools = FOOL’S) taken to task (ERRAND) (A FOOL’S ERRAND) for sending the newcomer for the bubble in the spirit level (A FOOL’S ERRAND)
6 The director’s handling of the play (TREATMENT) performed in The Theatre perhaps (TREATMENT in hospital theatre),
7 Most (w) of the trouble (row) (‘row’ without ‘w’ = RO-) at foreign gallery (-TATE) (ROTATE) is spin (ROTATE),
8 Something for someone who won’t be patient at night (DAY BED) in the guest quarters (DAY BED),
11 The one pulling the strings (PUPPET-MASTER) for boxer (PUP-), the favourite (-PET-) associated with 19 down (‘master’ = -MASTER) (PUPPET-MASTER)
15 Those taking a closer look (EXAMINERS) around (= reverse indicator) do a job for hatchet man (axe = EXA-) on those working on The Underground? (-MINERS) (EXAMINERS),
16 Refuses to deal with (BOYCOTTS) Toby Scot (Toby Scot) drunk (= anagram indicator) (Toby Scot = BOYCOTTS),
17 Get news (hear = HE-AR) about Bill (-AD-), for example (e.g. = -GE-), giving up (= reverse indicator) (HEADGEAR) a number of investments in Panama, or similar (Panama Hat = HEADGEAR),
19 Guru (MASTER) to half of those in 18 across (half of ‘MASTERstroke’ = MASTER),
20 Spies (CIA = CI-A) hiding rogue (rogue/cad = -CAD-) (CICADA) bug (CICADA),
23 Neighbours (UK-) lose the head (c) with lawsuit (‘case’ without ‘c’ = -ASE) (UKASE) with Fiat? (fiat/formal decree = UKASE).