Clues are in blue, with definitions underlined. Answers are in BOLD CAPS, then wordplay. (ABC*) means ‘anagram of ABC’. Deletions are in [square brackets].
Across
1 I’m a threat to all, promiscuous cleric said (5,6)
LOOSE CANNON: LOOSE=promiscuous, CANNON sounds like (“said”) CANON=cleric.
7 Member of Parliament‘s a dish: bachelor knocked out (3)
OWL: [b]OWL. I normally don’t have much time for contrived collective nouns, but “a Parliament of owls” is well enough known to make this definition delicious.
9 Act foolishly, hurling most abuse (4,5)
MESS ABOUT: anagram (“hurling”) of (MOST ABUSE*).
10 Wife visiting North American railway town (5)
CREWE: a CREE is a North American. Insert W for wife. I didn’t know Crewe is/was a railway town, but the wordplay convinced me.
11 Director of further education in damaging U-turn (7)
FELLINI: F.E. for further education, LLINI is IN ILL backwards (“U-turn”).
12 Pointless filibuster I leadenly can deliver (7)
STERILE: hidden answer (“delivered”).
13 Originally Ottoman fort half seen on numerous occasions (5)
OFTEN: fiddly parsing: O[ttoman] (“originally”), FT (fort), [se]EN (“half”).
15 Blissful state? Teacher doesn’t like it (9)
IGNORANCE: double definition, the second cryptic and a bit whimsical.
17 Passing Sian frolicking in river (9)
TRANSIENT: anagram of (SIAN*) “frolicking” in TRENT.
19 Bungling writer’s back, overcome by drink (5)
INEPT: NEP is PEN backwards, inside IT, an old-fashioned drink.
20 Say again: educated Liberal must go (7)
ITERATE: [l]ITERATE without the L[iberal].
22 If nurse is sick, one makes tea (7)
INFUSER: anagram of “sick” (IF NURSE*).
24 A Dickensian quirk? (5)
TWIST: double definition, the first being Oliver of course.
25 Somehow lure a girl, a freedom fighter? (9)
GUERRILLA: an anagram, “somehow”, of (LURE A GIRL*).
27 Retired academic gives signal of assent (3)
NOD: DON “retiring”.
28 One contemptuous of bards, and where they lie at rest? (5,6)
POETS’ CORNER: or, split differently, a POET SCORNER? It (but of course, not he) is in Westminster Abbey.
Down
1 Scottish smoker depressed, having to give up golf (3)
LUM: g[LUM] being depressed, without G[olf].
2 Resort to stuffing oddly oily bird (5)
OUSEL: USE in O-L-, the odd letters of OiLy.
3 Joy’s story recalled home full of love (7)
ELATION: ELAT is TALE “recalled”, then put O (love) in IN (home).
4 Australian with roots in Lincoln? (9)
ABORIGINE: ORIGIN in ABE.
5 Lines of attack rejected (5)
NOTES: the “rejected” attack is SET ON, backwards. “Lines” might be notes, as in “I dropped them a line”.
6 Kind of family that’s equivocal, putting university back (7)
NUCLEAR: equivocal is UNCLEAR. Move U for university as instructed.
7 Old piece of furniture niece destroyed, following instructions (9)
OBEDIENCE: O for old, BED is furniture, then IENCE is an anagram of (NIECE*) “destroyed”.
8 Interrogator may use this … or let deceit run riot? (3,8)
LIE DETECTOR: an anagram “running riot” of (OR LET DECEIT*).
11 Suffering from cold, TV interviewer attacked by dog (11)
FROSTBITTEN: David FROST was the interviewer, perhaps BITTEN by a dog.
14 Dealing with gas and ship’s propeller? (5,4)
TRADE WIND: TRADE=dealing, WIND=gas. The propellor of 19th century square-riggers bound to the Antipodes.
16 Crazy quality of Brazil, perhaps (9)
NUTTINESS: at first glance this looks like a double definition, but since CRAZY doesn’t seem to be the same part of speech as NUTTINESS, perhaps it’s just a cryptic definition.
18 Celebrated lamb producer in new venture (5-2)
START-UP: STAR=celebrated, TUP=bearer of lambs.
19 Conclude nothing can get to grips with northern hell (7)
INFERNO: INFER=conclude, O=nothing, all gripping N=northern.
21 Dog beginning to bound away, a born hunter (5)
EAGLE: the dog is a [b]EAGLE.
23 Sage quickly engulfing lake (5)
SOLON: SOON=quickly, L=lake. I knew SOLON by name, but no more. Turns out he was one of the “seven wise men of Ancient Greece”.
26 Make known dictator’s successor (3)
AIR: sounds like HEIR. (On edit: might sound like “heir” when listening to dictation.)
Edited at 2019-03-23 01:05 am (UTC)
Edited at 2019-03-23 01:32 am (UTC)
I did have a ? at INFERNO; since coming to grips with something is not gripping something, this seemed a bit loose as an inclusion indicator. I knew SOLON was a lawgiver, although I didn’t know of the 7 Sages; but I treated it as a common noun meaning ‘sage’–evidently this is a US usage only, and more specifically relating to legislators. As you can imagine, it’s not often used. If I recall correctly, the Sacramento baseball team in the Pacific Coast League back in the day was the Solons. I think they’re now the Mudlarks (that, by the way, is where Kevin Gregg the pitcher got his start).
Edited at 2019-03-23 03:28 am (UTC)
My only question mark was “lines” for NOTES, but now Bruce has pointed it out, I find “a short letter or note” for “line” in Chambers, and it all makes sense. I’m not sure I’ve ever really thought about the actual meaning of dropping someone a line!
A neat puzzle, with nothing contentious and no hold-ups.
FOI MESS ABOUT
LOI OBEDIENCE
COD EAGLE
TIME 9:16
Oh Mr. porter what shall I do
I wanted to go to Birmingham
But you’ve taken me on to Crewe….
I believe it was full of doubles entendres which were well above my head at the time.
Yes, this was a very nice one. That OWL thing always fools me. 14.18 including a lengthy sneezing fit and it’s not even pollen season yet.