I thought this was an elegant puzzle, the best on Wednesday for a while, not difficult but with some clever, smooth surfaces and no MERs for me. I went astray at first with 15a and took a while to sort out 21a, no issues with the rest in a total time of around 24 leisurely minutes. For a clue of the day I'd pick either 10a or 21a.

Across
1	Bank charge discount partially returned (4)
	SIDE - bank = side e.g. of a river. Reversed hidden in CHARG(E DIS)COUNT.
3	American embraces endlessly resilient old scientist (10)
	ASTRONOMER - There was discussion recently when we had AMER for American, and here it is again. Into AMER you insert STRON(G) (endlessly resilient) and O for old.
10	Describing open-air activities that could be yours to do (9)
	OUTDOORSY - (YOURS TO DO)*.
11	Tycoon is second victim of hoax, though losing just one pound (5)
	MOGUL - MO (second) GUL(L) victim of hoax loses an L.
12	Make fun of a politician in guise of a fool? (7)
	LAMPOON - A MP inside LOON = fool.
13	Guy at St Andrews? Liberal guy at St Andrews, not Conservative (6)
	LADDIE - A Scottish chap. The guy at St Andrews (R & A Golf Club of) is a CADDIE, carrying my bag, not C, add L.
15	Preparation the public can’t see for exclusion of NHS work? (7,8)
	PRIVATE PRACTICE - Cryptic double definition, where 'practice in private' wouldn't be seen in public. I went wrong for a while with PRIVATE MEDICINE, thinking the 'preparation' was a drug not an activity, but 6d ending in I woudln't work.
18	Landlord blocking theatre presented by cultivated political group (10,5)
	REPUBLICAN PARTY - PUBLICAN is our landlord, he goes into REP our theatre, then ARTY = cultivated.
21	Necklace queen’s wearing removed by force (6)
	TORQUE - I put in the correct answer to this quite a while before seeing how it worked; was the definition force or necklace? I think it is necklace, as TORE = removed by force, leaving you with QU for queen to insert. A torque (or torc) is a rigid metal necklace, as well as a force causing rotation.
23	Rewarding golf? Agonising missing first of putts (7)
	GAINFUL - G for golf, PAINFUL = agonising, loses its P.
26	Supple, seeing reduction of ailment in time (5)
	AGILE - AGE (time) has IL(L) inserted.
27	Area a lot choppy? Channel swimmer weak (2,1,3,3)
	AT A LOW EBB - (A A LOT)* then WEBB = Captain Matthew Webb, first to swim the channel in 1875. What a nice, topical surface, given the recent amazing feat by Sarah Thomas. A pity she didn't get sponsored to raise money for breast cancer research.
28	Lack of skill recording songbird? One gets exposed about that (10)
	INEPTITUDE - I NUDE = one gets exposed; into that insert EP (recording) TIT (songbird).
29	Times item in centre: several bits (4)
	BYTE - BY = times, multiplied by, TE = central letters of iTEm, a byte has 8 bits in it.

Down
1	Plunder harbour town, getting damper (10)
	SPOILSPORT - SPOILS = plunder, as a noun; PORT.
2	Information corporation supplied to American lawyer (5)
	DATUM - DA (American lawyer) TUM (corporation). Singular of DATA, which latter is all too often treated as singular not plural. A moment of pedantry.
4	Determined to include wild green island in African ecosystem (9)
	SERENGETI - My FOI. SET = determined, insert (GREEN)* and add I for island.
5	Though no son, optimistic over a line of monarchs (5)
	ROYAL - ROSY could be optimistic, delete the S for son, add A L(ine).
6	Mostly I refuse to accept degree of person who’s travelled (7)
	NOMADIC - I refuse could be "NO DICE", mostly = NODIC, insert MA degree.
7	Source of detailed view that is needed in review of farming (9)
	MAGNIFIER - Insert I.E. into (FARMING)*.
8	No opening for comic turn (4)
	ROLL - DROLL loses its opening letter.
9	Study leading to answer about golden solar gases (6)
	CORONA - CON (study) has OR (golden) inserted, then A for answer.
14	Playground: yard left cordoned off by rope, fit for repeated use (10)
	RECYCLABLE - REC = playground, Y = yard, CABLE = rope, insert L for left.
16	Pull together one million, supporting Society in contest (9)
	IMPROVISE - I, M(illion), PRO (supporting), then S for society inside VIE = contest.
17	Defending month being taken up in Bishop engaging in study (9)
	REARGUARD - READ = study; insert AUG reversed into RR (bishop) then insert that RGUAR into READ.
19	Happen to search for a legacy (7)
	BEQUEST - BE = happen, QUEST = search.
20	River being shown? It’s not what you’d want to drink (6)
	POISON - The River PO (in Italy) IS ON = being shown.
22	Praise X-ray as investment in unlimited health (5)
	EXALT - HEALTH "unlimited" = EALT, insert X for x-ray.
24	Passionate on-line exclamation of disapproval (5)
	FIERY - FIE! = exclamation of disapproval, is '"on line" i.e. on RY railway line.
25	Artist I’d upset about almost everything (4)
	DALI - AL(L) inside I'D reversed.

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