Across:
1 Observed (OBEYED) Old Bob (OB-) getting around Iris (-EYE-) with diamonds (-D) (OBEYED),
4 Siberian (Siberian = IBERIANS) criminal (= anagram indicator) living on Spanish border (IBERIANS),
9 Conventional type (FORMAL) of wild (= anagram indicator) flora (flora = FOR- AL) around motorway (-M-) (FORMAL),
10 Come (COM-E) across place (-PUT-) for right (-R) (COMPUTER) terminal (COMPUTER),
12 Fill the gap at The Mouth (CAP A TOOTH) – the person working on the bridge could do that (CAP A TOOTH),
13 Threatens to ignore rant (‘threatens’ to ignore’ rant’ = thees = SHEET) in the paper (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) of American (A) behind (= positional indicator) loss of face (SHAME) at waterworks (CRYING) (A CRYING SHAME),
21 Tiptoe away from pretentious (‘tiptoe’ away from ‘pretentious’ = renus = NURSE) surgeon’s assistant (NURSE),
22 A Room With a View perhaps (APARTMENT) produced by Studio (studio APARTMENT),
24 Be unsure (HESITATE) that man (HE-) is (is) retiring (= reversal indicator) (is = -SI-) from foreign museum (-TATE) (HESITATE),
25 Presumably a lot of people saw straight through (WINDOW) Casement (Casement sash WINDOW),
26 Follows in the footsteps of (RETRACES) cooks’ (=anagram indicator) caterers (caterers = RETRACES),
27 Type of arrangement (FLORAL arrangement) all for (all for = FLORAL) mischief (= anagram indicator).
Down:
1 Accepted (OFFICIAL) no threat in article of faith (no ‘threat’ in ‘article of faith’ = icloffai = OFFICIAL),
2 Turns up (= reversal indicator) nice road (Nice/French ‘road’ = rue = EUR-) is not closed (is open = OPE-N) around A- (-A-) (EUROPEAN) -scot? (EUROPEAN),
3 Cancel (axe = EXA-) review (= reversal indicator) by court (-CT) (EXACT) on the money (EXACT),
5 One of those at The Abbey (BROTHER -) is popular (-IN -) with the foreign (the = LA-) women (-W) (BROTHER-IN-LAW) related by marriage (BROTHER-IN-LAW),
6 Take back (REPOSSESS) off-colour (= anagram indicator) espressos (espressos = REPOSSESS),
7 The Star-Spangled Banner (US national ANTHEM) is obviously a type of country music? (ANTHEM),
8 Priest (priest = SPRITE) travelling (= anagram indicator) with amazing type who is a bit of a legend (SPRITE),
11 Lively sort (BOUNCY) on the board (CASTLE on chess board) (BOUNCY CASTLE) is full of gas at the present time and deflated afterwards (BOUNCY CASTLE),
15 Wild (= anagram indicator) roar (roar = OR-RA) over casket (-CHEST-) (ORCHESTRA), produced by one of those from the pit (ORCHESTRA),
16 Where some people go for their dates (CALENDAR) all year round, on paper (CALENDAR),
17 Attlee (Attlee = TEA T-EL) strangely (= anagram indicator) entertains old (-O-) women (-W-) (TEA TOWEL) employed in The Kitchen (TEA TOWEL),
19 Presents the news (ANCHOR) – there are no ties in chain store (there are no ‘ties’ in ‘chain store’ = chanor = ANCHOR),
20 Peter’s (peters = PRESET) plan (= anagram indicator) is arranged in advance (PRESET),
23 Pilot study (TRIAL) of trail (trail = TRIAL) mix (= anagram indicator).