Thanks to Hoskins for his usual fine clue surfaces. Definitions are underlined in the clues.
Across
1 Harmonise with Liberal breaking wind (5)
BLEND : L(abbrev. for a member of the Liberal Party) contained in(breaking) BEND(to wind;to turn round).
4 They produce small bloomers and S&M gear! (9)
COCKSPURS : At face value, something that might be extreme S&M gear!
Defn: …, flowers, that is, and not those garments that possibly could be associated with S&M.
They’re also the spurs on the legs of cocks and, unless Hoskins has an invention to share, S&M gear only if you’re a cock (rooster, to avoid misinterpretation). Hence I didn’t consider it a double definition.

9 Bolt chops and port (9)
DARTMOUTH : DART(to bolt;to dash off) + MOUTH(chops, in slang, as in “a blow in the chops”).
Defn: … in South Devon, England.
10 Dope one I love gets in Delft on vacation (5)
IDIOT : I(Roman numeral for “one”) + [ I + O(letter signifying 0;love in tennis scores) ] contained in(gets in) “Delft” minus all its middle letters(on vacation).
11 Coat Lady Penelope’s driver picked up (5)
PARKA : Homophone of(… picked up) “Parker”(Aloysius, chauffeur to Lady Penelope Creighton-Ward, in the TV series, Thunderbirds). He was also her butler, so the surface is apt.

12 What one might need after dodgy Cuban meal (9)
AMBULANCE : Anagram of(dodgy) CUBAN MEAL.
A WIWD (wordplay intertwined with definition) clue.
13 One of a series of dopes I messed about on E (7)
EPISODE : Anagram of(… messed) DOPES I plus(on) E.
15 Leaderless unit on military vehicle or vessel (7)
TANKARD : “yard”(a unit of length) minus its 1st letter(Leaderless …) placed after(on;tagged on to) TANK(a military armed and armoured vehicle).
18 Rotten broadcast got rid of portly comic Peter? (7)
DECAYED : Homophone of(broadcast) “de-Kay-ed”(a whimsical way of saying “got rid of Peter Kay, portly English comedian).

20 Hit relations, one’s a dim provincial type (7)
BUMPKIN : BUMP(to hit;to land a blow) + KIN(blood relations).
21 Leader of the pack with highest of hands? (3,6)
TOP BANANA : Taken literally, the highest member in bunches;hands of bananas.
23 Additional old paintings must be brought round (5)
EXTRA : EX-(prefix denoting old;former) + reversal of(… must be brought round) ART(paintings, etc.).
25 A pair of bishops could have books for him (5)
ABBOT : A + B,B(abbrev. for “bishop” twice;a pair of) plus(could have) OT(abbrev. for the Old Testament, books in the Bible).
Defn: One who is head of an abbey of monks, who might very well be visited by bishops bearing books.
26 Drunk, so a truant and I get really high! (9)
ASTRONAUT : Anagram of(Drunk) SO A TRUANT.
Defn: … in outer space, not high on drinks.
27 Already heated new ward MEP tours starts to really explode (9)
PREWARMED : Anagram of(new) WARD MEP containing(tours) 1st letters, respectively, of(starts to) “really explode“.
28 Come on over (gents getting naked for starters) (5)
ENTER : Reversal of(… over) RE(on;with reference to) placed after(… for starters) “gents” minus its 1st and last letters(getting naked).
Down
1 One who’s crashed might be covered with it (9)
BEDSPREAD : Cryptic defn: “crashed”;went to sleep as in “he crashed immediately after the party”.
2 No time for fear? That’s a mistake! (5)
ERROR : “t”(abbrev. for “time”) deleted from(No … for) “terror”(fear).
3 Curse someone like Bojo, being critical (9)
DAMNATORY : DAMN(to curse) + [A TORY](someone like Bojo, nickname for Boris Johnson, a member of the Conservative Party).
4 An old make of beer bottle (7)
COURAGE : Double defn: 2nd: The nerve needed to do something difficult or dangerous.

5 Share digs about old and rather grasping husband (7)
COHABIT : C(abbrev. for “circa”;about or approximately when referring to dates) +O(abbrev. for “old”) plus(and) [A BIT](rather;to a certain degree, as in “it’s rather painful to hear”) containing(grasping) H(abbrev. for “husband”).
Defn: …;accommodation.
6 Quiet place one might get a drop of whiskey (5)
STILL : Double defn: 2nd: A synonym for “distillery” where whiskey, say, is produced.
7 Flag, having sex by the Dee? (5,4)
UNION JACK : UNION(the act of being united in sexual intercourse) + JACK(Dee, English comedian).

8 French scorer posed by exit with top off (5)
SATIE : SAT(posed for, say, a painting or a photograph) plus(by) “die”(to exit this life) minus its 1st letter(with top off).
Answer: Erik, French composer of musical scores.
14 Helplessly drunk and impotent (9)
INCAPABLE : Double defn: 2nd: Unable to take effective action.
And one part of the clue might be the result of the other.
16 Very successful track for the Boss (6,3)
NUMBER ONE : Double defn: 1st: …, that is, a music track in the hit parade.
And the clue’s surface is true of the Boss, nickname for Bruce Springsteen.
17 Fellow actors right to tour English town (9)
DONCASTER : DON(a fellow;a member of the teaching staff at a university) + CAST(the group of actors in a specific play) + R(abbrev. for “right”) containing(to tour) E(abbrev. for “English”).
Defn: … in South Yorkshire, England.
19 A male dread possibly could be loss of sensation in member! (4,3)
DEAD ARM : Anagram of(… possibly could be) [A + M(abbrev. for “male”) + DREAD].
20 Blooming keep going in the sack! (7)
BLASTED : LAST(to keep going;to endure) contained in(in) BED(the sack;a place for sleeping or having sex in, as in “she was good in the sack”).
Defn: …, as an expression of annoyance, as in “that blooming teacher gave me an F”.
21 Bum President making you mad essentially (5)
TRAMP : “Trump”(current US President) with “u”(letter representing “you”, as in text messaging, say, or in Sinead O’Connor’s song) replaced by(making …) middle letter of(… essentially) “mad“.
And he does have that effect on many people.
22 Those leading around stockcar track ram another car (5)
ASTRA : 1st letters, respectively, of(Those leading) “around stockcar track ram another“.
Defn: … engineered and manufactured by Opel, German carmaker.

24 Drink brought round when? For this, perhaps (5)
TOAST : TOT(a small amount of strong alcoholic drink) containing(brought round) AS(when, as in “look around when you enter the room).
Defn: A call to a group to raise their glasses and drinks in honour of someone or something.
A WIWD clue.
Although for me, this didn’t seem up to his normally very high standard, it was still very entertaining. My personal favourites were 4a and 19d.
Thanks to Hoskins and scchua.
Some flashes of the ‘old’ Harry in this one but I can’t help thinking that he’s given up the Babycham sessions!
An enjoyable puzzle nevertheless.
Thanks to Hoskins and to scchua for an excellent blog.
A not too strenuous solve for a Sunday. One or two we couldn’t parse but were obvious from definition and/or crossing letters. We did wonder if ‘bum’ was doing double duty in 21d (as definition and identifying which president was referred to) and our collective mind boggled about the S&M gear in 4ac. As for 4dn, ‘Courage’ may be an old “make” of beer in that the Courage brewery is long gone but Courage Directors and other beers with the Courage name are still brewed elsewhere by others.
Favourites were PARKA and BUMPKIN.
Thanks, Hoskins and scchua.
Unlike some above, I found this crossword almost a return to how he used to be.
Quite a lot of surfaces with references to his favourite subjects: sex, drugs and booze. No HerMaj in sight, though. Perhaps, the final bit of crudeness was missing but non the worse for that as far as I’m concerned. This was surely much more like the ‘old Harry’ than in his Slormgorm guise.
Meanwhile, the clueing was very tight and impeccable.
The AMBULANCE clue of 12ac raised a particular (big) smile.
Many thanks to scchua & Hoskins.
ps, I’ve noticed (and said) it before. Our setter seems to love grids with a cross in the middle, one which some setters call an FT grid. His puzzle in today’s Sunday Times (under his ‘real’ name) has one too!
COCKSPURS was a guess-and-check. Didn’t know the flowers.
Thanks for the parsing of DECAYED – gah!
I certainly found here flashes of Harry at his most himself, if not at full trolleyload-of-babycham levels. Loved UNION JACK and BLASTED.
Many thanks Hoskins and scchua.
P.S. Interesting bit of trivia about the crosses in the grid, Sil. Not sure what to make of that!