Across:
1 Without a leader (m), mob ('mob' without 'b' = OB-) took a view (-EYED) (OBEYED) and followed (OBEYED),
4 People from Spain and Portugal (IBERIANS) and Serbia in (Serbia in) trouble (= anagram indicator) (Serbia in = IBERIANS),
9 Shut out (FORGET) of Smith’s place (FORGE-) on square (-T square) (FORGET),
10 Come (COM-E) across place (-PUT-) that’s verging on the ridiculous (verging on the ‘Ridiculous’ = -R) (COMPUTER) and PC (COMPUTER),
12 Work with one of those working on The Crown (CAP A TOOTH) – the woman working on The Bridge could do that (CAP A TOOTH),
13 Paper (SHEET) by that man (-HE-) in class (set = S-ET) (SHEET),
14 One is extremely tense (A BAG OF NERVES) holding the butterflies presumably (A BAG OF NERVES),
18 Terrible bad luck (A CRYING SHAME) for authority opening (‘Authority’ opening = A) waterworks (CRYING) linked to phoney (SHAM-) energy (-E) (A CRYING SHAME)
21 Edited (o) local paper (Indo) (‘indo’ without ‘o’ = IND-) that is (i.e. = -IE) (INDIE) created by one of those not part of the mainstream (INDIE),
22 Includes A Room With a View perhaps (APARTMENT) produced by Studio (studio APARTMENT),
24 Think twice about (HESITATE) anaesthetist knocking out ants (‘anaesthetist’ knocking out ‘ants’ = aehetist = HESITATE),
25 In retrospect (= reversal indicator) nice street (Nice/French ‘street’ = ‘rue’ = -EUR) with the odd snoopy (the odd ‘SnOoPy’ = sop = POS-) (POSEUR) exhibitionist (POSEUR),
26 Fears are (fears are) unnatural (= anagram indicator) (fears are = SEAFARER) to old sailor (SEAFARER),
27 Safest (safest) arrangement (= anagram indicator) (safest = FEASTS) for religious ceremonies (FEASTS).
Down:
1 It's accepted by the authorities (OFFICIAL) there is no threat in article of faith (no 'threat' in 'article of faith' = icloffai = OFFICIAL),
2 The Irishman (EUROPEAN) who is a Union member? (EUROPEAN member of European Union),
3 Put in office (ELECT) that’s top of the range (select) starting off (s) (‘select’ without ‘s’ = ELECT),
5 One of those at The Abbey (BROTHER-) is popular (-IN -) with the foreign (‘the’ foreign/French= LA-) women (-W) (BROTHER-IN-LAW) related by marriage (BROTHER-IN-LAW),
6 Order (= anagram indicator) espressos (espressos = REPOSSESS) to take back (REPOSSESS),
7 Man in the street losing interest (‘man in the street’ losing ‘interest’ = manhet = ANTHEM) in country music (ANTHEM),
8 Walks like a peacock (STRUTS) in line from turnstiles (‘line’ from ‘turnstiles’ = tursts = STRUTS),
11 It’s inflated at the present time (BOUNCY CASTLE) in one of those blown up fortresses? (BOUNCY CASTLE),
15 Wild (= anagram indicator) roar (roar = OR-RA) getting to grips with casket (-CHEST-) (ORCHESTRA) produced by one with a job down in pit? (ORCHESTRA),
16 They provide courses (CATERERS) for those employed by The Party (CATERERS),
17 Happy to be dismissed by supply teacher (‘happy’ to be dismissed by ‘supply teacher’ = sultecer = LECTURES) producing stern reprimands (stern reprimands = LECTURES),
19 When they’re switched on you’ll see these (LIGHTS) slight (slight) changes (= anagram indicator) (slight = LIGHTS),
20 Party (do = OD-) over (= reverse indicator) seas (seas)? Possibly (= anagram indicator) (seas = -ESSA) (ODESSA) in Ukrainian port! (ODESSA),
23 The irony is (TROPE), acting company (troupe) is missing you (you), it’s said (= homophone indicator)? (‘you’ = u) (‘troupe’ without ‘u’ = TROPE).