So so hard, but just brilliant too. Thanks setter! Up with this kind of thing!
1 Royal couple making double echo over disturbing broadcast (8)
QUONKING – QUEEN + KING [royal couple], making its EE [double Echo] into O [over]
5 Ghost essentially appearing where feast is cut short, twice? (6)
BANQUO – {gh}O{st}, appearing at the end of BANQU{et}, &lit
10 One who “maximises” each height, height embracing possibly dull lives (15)
APOPHTHEGMATIST – A POP [each] + HT HT [height | height], “embracing” EG MAT IS [possibly | dull | lives]. One who “maximises” as in, “constructs maxims”.
11 Reclusive teen and I stun pollsters on short walk (10)
HIKIKOMORI – I K.O. MORI [I | stun | pollsters] on HIK{e} [“short” walk]
13 Hardly an Arabian man suggesting forgiveness? (2,2)
AS IF – Asif is a masculine Arabian name, literally meaning “forgiveness”.
15 Demolish ickiest of human settlements (7)
EKISTIC – (ICKIEST*) [“demolish…”]
17 Previously checked Poles were going out (7)
SNEBBED – S N [(both) Poles] + EBBED {were going out]
18 Related partial U-turn of CTC to those sending signals? (7)
COGNATE – hidden reversed in {charli}E TANGO C{harlie}
19 Desire abnormal purge after census (7)
LUSTRUM – LUST RUM [desire | abnormal]
21 Born fairly recently, having heart defect, feeling cold in some parts (4)
NESH – NE{wi}SH [born fairly recently, with defective “heart”]
22 Part of gullet in oryx, one without parents taking irregular turns? (10)
OROPHARYNX – interleave ORPHAN [one without parents] with ORYX irregularly
25 Not having enough excitement to grip European, a road somewhere in Bedfordshire (8,7)
LEIGHTON BUZZARD – LIGHT ON BUZZ [not having enough excitement] to “grip” E [European], + A RD [a | road]
27 Opening of Bard’s own Shakespearean club (6)
BALLOW – B{ard} + ALLOW [own]
28 Poet’s rule about verse is extremely bombastic? (8)
SOVRANTY – about V [verse] is SO RANTY [extremely bombastic?]
DOWN
1 Caribbean provincial, apparently one subjected to suppression (7)
QUASHEE – also humorously suggesting “one who is quashed”
2 Mixed-load carrier with breadth limited by wheel shapes (3)
OBO – B [breadth] “limited by” O O [(two) wheel shapes]
3 Relaxed briefly under exotic khaki and white pines (10)
KAHIKATEAS – AT EAS{e} [relaxed “briefly”] under (KHAKI*) [“exotic”…]
4 Bring up Canadian media theorist, then dismiss leftcentre prophet (5)
NAHUM – M{cl}UHAN first reversed, and then losing L C [left | centre]
6 Nanny’s answer affected toff (4)
AYAH – A YAH [answer | affected toff]
7 Royal attendant overlooking leader keeps inches away, lifting blackcurrant plant (6-5)
QUINSY-BERRY – {e}QUERRY [royal attendant “overlooking leader}] “keeps”: INS [inches] + BY reversed [away “lifting”]
8 Terrible discomfort, losing every third in multiple divisions (7)
OCTOFID – (DI{s}CO{m}FO{r}T*) [“terrible…”]
9 Left my aunt to go north, collecting East Germany’s fabulous ash (8)
YGDRASIL – L + I SAY [left | my aunt!] reading from south to north, “collecting” GDR [= German Democratic Republic, the official name for East Germany]
12 Combination of likes and gripes in a form of chess (11)
KRIEGSSPIEL – (LIKES + GRIPES*) [“combination of…”]
14 Rude noise that’s surprising famous person upending huge wine bottle (10)
BELSHAZZAR – RAZZ AH SLEB [rude noise | that’s surprising! | famous person] reversed
16 Opposite of his little snags? (8)
CHEERIOS – The opposite of “hi” being “cheerio”, then pluralise! Snags and cheerios are both Antipodean words for sausages.
18 Cross meeting lack of firmness in jaw (7)
CONFLAB – CON [cross] meeting FLAB [lack of firmness]? Unless it’s C ON [cross | meeting], but I would have thought cross was more likely to be abbreviated as X…
20 Erase fifth letter in a jumble involving third square in anagram form? (7)
MIXEDLY – MEDL{e}Y [a jumble, with its fifth letter “erased”], “involving” IX [third square, after I and IV]
23 Catering chain sinking billions into turning drink container round (5)
PUBCO – sink B [billions] into reversed CUP [“turning” drink container] + O [round]
24 Jerk with resistance measures switching extremes (4)
SHMO – OHMS [resistance measures], swapping its first and last letters
26 Glaswegian personal trainer shedding two layers? (3)
AIN – {tr}AIN{er}, losing not just its first and last letters, but its second and penultimate too
Small typo in 12dn, the setter has used an alternative spelling (that I have never previously seen): kriegsspiel
re 18dn, Collins has, for cross: “16. slang; a fraud or swindle” which seems to work.
I did like 25ac.
Just to prove I read V’s comments (for entertainment as much as enlightenment): the East Germany reference in 9d, is GDR, though it was always DDR on the stamps.
Then again, YGDRASIL, fabulous ash, perhaps one of the better known ridiculous spellings.
Sub note. Why does the spellchecker want Bedfordshire to be Hertfordshire (sic)? I can more easily understand its preference for Futon.