Across:
1 Come across abandoned room (‘come across’ abandoned/ without ‘room’ = ceacss = ACCESS) with permission to enter (ACCESS),
4 Barrister (SC-) is (-IS-) so (-SO-) right (-R-) – society (-S) (SCISSORS) is capable of cuts at the top (SCISSORS),
9 Protesting tactics (LIE INS) for starting 22 across (‘lie in wait’ = LIE) at fashionable (IN-) school (-S) (LIE INS),
10 Most of (e) the allergic reaction (‘sneeze’ without ‘e’ = SNEEZ-) in (-IN-) front garden (front ‘garden’ = -G) (SNEEZING) is a sure sign someone is under the weather (SNEEZING),
12 Pay no attention to (IGNOR-E) introductions to a new chapter (introductions to ‘a new chapter’ = -ANC-) inside (IGNORANCE) Lack of Intelligence (IGNORANCE),
13 Sent (sent = TENS-) off (= anagram indicator) for Spain (-E) (TENSE) in a state of agitation (TENSE),
14 A number of those taking job of Ceann Comhairle (HOUSEMASTERS) keeping an eye on the childish types (HOUSEMASTERS),
18 Access Twitter (GET A HANDLE ON) to recover one’s self control (GET A HANDLE ON)
21 Cause trouble (ACT UP) offering a (A-) college (-C-) place (put = -T UP) in retrospect (= reversal indicator) (ACT UP),
22 Lounge (LIE) has fashionable (IN) job for those talking orders (WAIT tables) (LIE IN WAIT) – it will require one to be patient before onslaught begins (LIE IN WAIT),
24 Church (CH-) woman (-ANNE-) left (-L-) school (-S) (CHANNELS) for The Stations (CHANNELS),
25 They leave bright-eyed type (‘they’ leave ‘bright-eyed’ = briged = BRIDGE) going across The Liffey (BRIDGE),
26 Awful (= anagram indicator) ordeal (ordeal = EL DORA-) for party (-DO) (EL DORADO) in place of great wealth (EL DORADO),
27 Criminal (= anagram indicator) dealer (dealer = LEADER) for The Don, for example (LEADER).
Down:
1 It’s okay (ALL RIGHT) as there’s nothing left perhaps (ALL RIGHT),
2 Respectable type (CLEAN-CUT) of college (C-) gets meagre (-LEAN-) piece of the pie (-CUT) (CLEAN-CUT),
3 Presumably echoes what old bats are capable of (SONAR) with business partner (e.g., “Father & Son” = SON-) from America (-A-) opening restaurant (opening ‘restaurant’ = -R) (SONAR),
5 Pay attention to (CONCENTRATE-) The Last Word (the last ‘word’ = -D) (CONCENTRATED) – it’s the epitome of deep thought (CONCENTRATED),
6 Protected (SHELTERED) the elders (the elders = SHELTERED) all over the place (= anagram indicator),
7 Knowing one’s stuff (knowing one’s ONIONS) could make one cry (ONIONS),
8 Endorsed (SIGNED) new (= anagram indicator) design (design = SIGNED),
11 A foreign (a = UN-) friend (pal = -PA-L-) admits writing (from the 3Rs = -R-) to Ella (Ella = -ALLE-), setting up (= reversal indicator) journalist (-ED) (UNPARALLELED) with something unique (UNPARALLELED),
15 In the middle of storm, centre (EYE- of the storm) gets the first score (-OPENER) (EYE- OPENER) – it’s astonishing to one of the viewers (EYE-OPENER),
16 Put the foot down (DEMANDED) for worker (-MAN-) from department? (-D-) Indeed! (‘in’ indicates ‘man’ + ‘d’ is inside ‘deed’ = DE-ED) (DEMANDED),
17 Paraphernalia (K-IT-) includes new (new = -N-) exhibit (-WEAR) (KNITWEAR) from Jersey (jersey = KNITWEAR),
19 Government attends UN summits (‘government attends UN’ summits = GAU-) with revolutionary (-CHE) (GAUCHE) lacking in the social graces (GAUCHE),
20 Hadn’t a (hadn’t a = AT HAND) breeze (= anagram indicator) it’s readily accessible (AT HAND),
23 Tribunes missing bit (‘tribunes’ missing ‘bit’ = runes = NURSE) of care (NURSE).