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A standard Quiptic, made simpler, for me at least, by the many anagrams. Thanks to Beale, who is not a frequent setter here. Definitions are underlined in the clues. [[The pictures at the bottom have unidentified links to the puzzle. Please enclose any comments on them in double brackets. Thank you.]]
Across
1 Authenticity of early IT development (7)
REALITY : Anagram of(development) EARLY IT.
5 Agree adjustment to student year with alacrity (7)
EAGERLY : Anagram of(adjustment) AGREE plus(to) L(abbrev. for “learner”;student) +Y(abbrev. for “year”).
10 Advanced alternative, say, in modern times (4)
AGED : Anagram of(alternative) “E.G.”(abbrev. for exempli gratia;for example;say) contained in(in) A.D.(abbrev. for “anno Domini”;to denote years in modern times).
11 Requiring power to let a cleric off (10)
ELECTRICAL : Anagram of(off) LET A CLERIC.
12 Point of scandal engulfing the City (6)
DIRECT : DIRT(slang for scandalous information;gossip) containing(engulfing) EC(postcode for London area, regarded as the financial and commercial centre).
Answer: To point someone to a certain, well, direction.
13 Get right part for radio (8)
RECEIVER : RECEIVE(to get, not as good as to give?) + R(abbrev. for “right”).
Answer: The equipment in a radio (set) that receives and converts electrical signals into sound.

14 Cast doubt on church claim about one point (9)
CHALLENGE : CH(abbrev. for a church building) + ALLEGE(to claim without it having been proven) containing(about) N(a compass point)
16 Mixture of ancient English (5)
PASTE : PAST(of very long ago;ancient) + E(abbrev. for “English”).
17 Waterlogged land damages hotel (5)
MARSH : MARS(damages;spoils) H(represented by “hotel” in the phonetic alphabet).
19 Pieces broken by French spies found around motorway (9)
FRAGMENTS : FR(abbrev. for “French”) AGENTS(short for secret agents;spies) containing(found around) M(abbrev. for “motorway”, eg. the M1).
23 Low point of man beset with confusion (8)
BASEMENT : Anagram of(with confusion) MAN BESET.
24 Bill’s only change (6)
ADJUST : AD(short for “advertisement”, an example of which is the bill;paper and such with promotional material on it) + JUST(only, as in “It seems like it was just yesterday that he spotted her when she was only a cocktail bar waitress”).
26 Celebrated socialist took in English politician (10)
REMEMBERED : RED(a socialist, from the colour historically associated with leftists and communists and the like) containing(took in) { E(abbrev. for “English”) MEMBER(of Parliament;a politician) }.
Answer: Celebrations in remembrance of;to mark a historical event, eg. a religious one.
27 Weak-sounding stream (4)
POUR : Homophone of(sounding) “poor”(weak;deficient). A pronunciation that is an alternative to “poo-er”.
Defn: As a verb.
28 Just hit on ending to fox journalist (7)
BRUSHED : BRUSH(the tail of;the ending to a fox) + ED(abbrev. for “editor”;a journalist). An0 Just hit;touched with only slight contact.
29 Serious attention given to refuge (7)
EARNEST : EAR(attention, as in “lend me your ears”) plus(given to) NEST(a place of refuge, especially if you were lovers).
Down
2 Hard to single out particular nationality (7)
ENGLISH : H(abbrev. for “hard”) placed below(to, in a down clue) anagram of(out) SINGLE.
3 Left furthest part of rocky projection (5)
LEDGE : L(abbrev. for “left”) EDGE(the furthest part;the border).
4 Drama of Mad Hatter’s final performance (7)
THEATRE : Anagram of(Mad) HATTER + last letter of(final) “performance”.
6 Shenanigans opposed by civil service (6)
ANTICS : ANTI(opposed to;against) plus(by) CS(abbrev. for the Civil Service).
7 Over a mile to get home, having dined with dispatch (9)
ELIMINATE : Reversal of(Over, in a down clue) MILE plus(to get) IN(at home;not out) plus(having) ATE(dined;eaten).
Answer: To murder;to dispatch.
8 List set to reform the most unproductive (7)
LEANEST : LEAN(to list;to slant towards the side) + anagram of(to reform) SET.
Answer: Especially with regard to livestock or mineral ore.
9 Judge equipment with time to sort out storage facilities (13)
REFRIGERATORS : REF(short for “referee”;a judge) + RIG(equipment;gear) plus(with) Edit.note: T(abbrev. for “time”) + anagram of(to sort out) STORAGE ERA(long period of time) plus(to) anagram of(out) SORT. Thanks Offspinner.
Answer: Facilities for cold storage.
15 Radio audience play silent Cupid when love is absent (9)
LISTENERS : Anagram of(play) SILENT + “Eros”(the god of love in Greek mythology, or Cupid in the Roman version) minus(when … is absent) “o”(the letter that looks like 0;love in tennis scores).
Answer: Those gathered round a receiver.
18 Unprofessional of a graduate with true potential (7)
AMATEUR : A MA(abbrev. for “Master of Arts”, a degree a graduate might have) plus(with) anagram of(potential) TRUE.
20 Relative force led to dam collapse (7)
GRANDMA : G(abbrev. in physics for the force of gravity) + RAN(managed;led, say an organisation) + anagram of(collapse) DAM.
21 Leading truck has problems with wipers (7)
TISSUES : First letter of(Leading) “truck” plus(has) ISSUES(problems;unresolved matters).
Answer: Pieces of soft paper to wipe with.
22 Rock fall by lake during exercise (6)
PEBBLE : { EBB(to fall;to decrease in, say, intensity) plus(by) L(abbrev. for “lake”) } contained in(during) PE(abbrev. for “physical education”;exercise).
Answer: A small rock;a rounded stone worn smooth by water erosion.
25 German agreement to censure another nation (5)
JAPAN : JA(German for “yes”;agreement) plus(to) PAN(to censure;to criticise severely, eg. a performance).
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Thanks, scchua.
I thought 9 across was REF + RIG + ERA (=time) TORS (anagram of sort).
Thanks Offspinner, you’re right of course. Blog amended.
I enjoyed this Quiptic by Beale. My favourites were 7d, 20d, 23a, 4d, 12a, 14a.
Thanks for the blog, scchua.
Nice Quiptic from Beale.
Thanks scchua; I particularly enjoyed BRUSHED.
[[The quiz is more challenging than the puzzle. So far:
#3 is DCI Roderick Alleyn found in the detective series by Ngaio MARSH
#6 is GRANDMA Moses – an American folk artist
#8 is PEBBLE Beach
Is the Alec Guinness {#9} connection to Bridge over the River Kwai directed by David LEAN (or to Oliver). Lean also planned a film about Ghandi where BEN KINGSLEY {#7} starred in the Richard Attenbrough production. Ron Moody (#4) also played Fagin in the stage production of Oliver.
What the lingerie American football team is doing here is anybody’s guess, although they are quite easy on the eye……..]]
[[Maigret and Poirot in the stamp {#1} might be chasing FRENCH SPIES??]]
[[Hi Robi. 3, 6 and 8 are correct. 4 is Ron Moody, but what’s the connection? Hint: the pics between them share links to 4 of the answers in the puzzle.]]
Thanks to Beale for the puzzle and scchua for the blog.
[[Picture #2 is a wide RECEIVER being stopped by a g-string tackle.]]
Cheers…
[[Fagin is a RECEIVER of stolen goods and has been played by Moody, Guinness and Kingsley]]
[[Patrick Marnham won the 1993 MARSH Biography Award for “The Man who Wasn’t Maigret {#1}: A Portrait of Georges Simenon” ??]]
[[#1 the ‘detective fiction’ stamps included a set in honour of Ngaio MARSH
Assuming grandpuzzler @7 is correct about RECEIVER, that just leaves the picture of HMS VICTORY, which has no link at present]]
[[Well done, Robi and grandpuzzler. That leaves #1 and #5. I think you’re overcomplicating #1.]]
[[The wreck of the HMS Victory has recently been found, but all items have to be reported to the RECEIVER of Wreck – is that it????]]
[[Detective Fiction includes MARSH??]]
[[Yes Robi! There is a position in the Maritime and Coastguard Agency called the Receiver of Wreck. And Marsh, one of the Queens of Crime, writes detective fiction.]]