A pretty easy start with the top line going straight in flattered to deceive, and I took a hard-worked 29 minutes over this. Wordy clues needed much wrangling especially to tease out the wordplay, which I needed to do to verify sometimes flaky entries. I knew one of the two composers, but the other only as the first name of the Russian Ripsmecorsetsoff, who spelled it differently. There’s some petrology you may have to make up from available fragments, some Latin you may have to take a running jump at, and a couple of other words which might increase the scope of your vocabulary. I have tried to supply relevant dictionary and Wiki notes to back up my assumptions. I did like the furniture company undercutting the most end of end of season DFS sale.
Clues are thus, definitions so, and solutions WRIT LARGE
1 A poignant novel about a South American (10)
PATAGONIAN A nice, cheerful anagram (novel) to start us off: A POIGNANT and A your letters to reshape
6 Go to the Highlands for a party (4)
GANG Some Scots for you, might as well be Burns: “And I will luve thee still, my dear, Till a' the seas gang dry.” Whatever, go translates to gang, and I suppose a party of (say) bricklayers is a gang
10 Calendar produced by charity — short collection about to follow (7)
ALMANAC Charity is ALMS which you cut short, and add ANA for collection (of someone's table talk or of gossip, literary anecdotes or possessions – Chambers) and C for about, as in Circa
11 Smaller region of Australia recalled when crossing plain (7)
SUBAREA Australia is represented by AUS, reversed and “crossing” BARE for plain.
12 Impressive sticker backing large theatre university inserted in petition (9)
SUPERGLUE I think this works as LG for large, REP for theatre and U for University all reversed (backing) in SUE for petition. Only resolved post solve, partly because of the unusual (but verified in sources) abbreviation for large
13 Girl staying in until daybreak (5)
TILDA Today’s hidden (and first random female) “staying in” unTIL DAybreak. Swinton the only one to spring to mind.
14 Something in the blood, etc, stirring Laurel on vacation (1-4)
T-CELL “A type of lymphocyte involved in cellular immunity, that matures (in mammals) in the thymus gland” An anagram (stirring) of ETC plus the LL that results when you empty Laurel. Only CELL emerges as a likely word, leaving the T to be the introductory letter.
15 By that time, opening a ridiculously cheap furniture business! (4,5)
IPSO FACTO your ridiculously cheap furniture business is a IP SOFA CO., T(ime) opens by finding a place towards the end. Today’s Latin
17 Masses of religious lessons to be taken from Plato’s work (3,6)
THE PUBLIC Today’s (sort of) Greek is Plato’s THE REPUBLIC, from which you remove R(eligious) E(ducation)/lessons
20 Brit abroad disregarding British, goodness me! (5)
LIMEY Abroad being the US of A, primarily. Goodness me is BLIMEY from which the B for British is “disregarded”
21 In intelligence matters, not reaching Q? (2,3)
UP TOP, the definition closely mirroring Chambers “in the head, in respect of intelligence”. Not reaching Q is UP TO P, of course.
23 Leaves factory’s daily grind (5,4)
PAPER MILL I have visited Glen Mills PA, site of the paper mills that “supplied the United States government with a special, patented paper for the printing of government bonds and notes”. Nothing much remains of this once-significant site but a few broken walls and a plaque. Here we have a charade of daily (news)PAPER and grind: MILL (as in pepper)
25 Special forces, mostly veteran, supplying fairweather protection (7)
PARASOL The special forces are PARAS, and most of veteran is OL(d)
26 Major venue, part of summer activity in the West End (7)
AUGUSTA Home of The Masters golf tournament, one of the four “majors”. Part of summer is AUGUST, and the rest of the clue is a convoluted way of indicating A, on the west end of Activity.
27 Reflecting ruby, ultimately linked with pearls (4)
DEWY Reverse (reflecting) of the last letter (ultimately) of ruby plus WED for linked. That leaves the definition as “with pearls”. I have found an image of a “dewy cobweb with pearls from raindrops”. Will that do?
28 Like piper getting a note right: another is flat (4-1-5)
PIED-A-TERRE A rather famous piper was PIED, add A note: TE, R(ight) and another note RE
1 Is solicitor’s power something 25 deflects? (5)
PRAYS P(ower) plus RAYS which would be deflected by 25’s PARASOL. This helped me get 25 rather than the other way round
2 Magazine article one reads for hours (9)
TIMEPIECE The magazine is the venerable TIME, and article just PIECE. A rather whimsical definition
3 Versatile soldier and sailor breaking contract (7-7)
GENERAL-PURPOSE Which makes the soldier a GENERAL, the sailor a PO (Petty Officer) and (to) contract PURSE (as lips)
4 German who scored Bayern’s last two clutching fizzy drink (7)
NICOLAI Scorers are often composers hereabouts. Bayern’s last is N, two is (are?) II, and COLA the fizzy drink “clasped”. Contemporary with Verdi, though he died 50 years before the master, he was at one time more popular in Italy than Giuseppe. Carl Otto Ehrenfried Nicolai, three quarters of whose name looks much more German, was most famous for his opera “Die lustigen Weiber von Windsor” based on guess which Shakespeare play.
5 One has matter in hand? Shilling on tax (7)
ABSCESS I think the hand is an AB (seaman) S is from Shilling and tax is CESS, rather an obsolete version. In medical terminology, matter is pus, content of an abscess.
7 Hearing warning of attack, left (5)
AURAL I wasn’t at all sure of AURA as a synonym for warning of attack, but Chambers gives “the peculiar sensations that precede an attack of epilepsy, hysteria, or certain other ailments” so that’s fine. Add L(eft)
8 Flight of Greek girl affected Troy (9)
GRADATORY The wordplay is GR(eek) ADA (random girl) and affected/anagram TROY the rest. Collins gives what Chambers doesn’t, the noun as a flight of stairs
9 Outstanding leader deserting Labour: one to sink the Tories (1,3,2,3,5)
A BIT OF ALL RIGHT Respaced, it’s leaderless LAB I (one) TO FALL (sink) RIGHT (the Tories). I’ll leave you to work out who the outstanding Labour leader capable of trouncing the Conservatives might be. I could not possibly comment.
14 I got in three tangos and Rose pranced (9)
TITTUPPED Other spellings are available, but the sort of prancing that horses in particular do. I is (am?) inserted into TTT (three NATOs), and rose (ignore the capital) represents UPPED: “he upped/rose and went.”
16 Official party had launched 2001 Oscars (9)
COMMISSAR “Launch” MMI (2001 in Latin) with OSCARS
18 Rock fragments thrown from stage indisposed one (7)
LAPILLI Bits of rock chucked out of volcanoes, apparently. Trust the wordplay, stage is LAP, indisposed ILL and yet another I one.
19 The world of the busy composer (7)
COPLAND Old hands will know a busy is a police officer (19th century slang) so the world of the busy is COPLAND. Aaron (Fanfare for the Common Man) is the American composer.
22 Rattle, blanket or sling (5)
THROW A triple definition, a throw being a blanket designed to cover a piece of furniture.
24 Let out of jail, finally relax (5)
LEASE That sort of let out. Last letter (finally) of jaiL plus relax: EASE