Across
Contemptible? That's quite probable (4,2,3)
I haven't cracked this one yet — but Fifteensquared have:
I’m not sure about this: it seems like a double definition but I can’t quite work out the first one (contemptible?) Contemptible indeed : LIKE A SNOT – thanks to the first few commenters
European male with female outside, muscular types (2-3)
I haven't cracked this one yet — but Fifteensquared have:
HEN (female) round E (European) M (male)
Reported as reporter, say (5)
Means to test rule – I expect no changes (9)
I haven't cracked this one yet — but Fifteensquared have:
An anagram (changes) of I EXPECT NO – a reference to the saying, ‘It’s the exception that proves (tests) the rule’
Property of some numbers – remove pairs and one remains (7)
I haven't cracked this one yet — but Fifteensquared have:
If we remove the double letters – DD and SS – we’re left with ONE Edit: It’s apparently cleverer than that – see Monkey @ 33, 34, 36 (Brendan is a mathematician!)
Lacking direction, I am trapped in area? Not so (7)
I haven't cracked this one yet — but Fifteensquared have:
I’M (I am) in A (area) + LESS (not so)
Turn off none? That's plain (5)
I haven't cracked this one yet — but Fifteensquared have:
A reversal (turn) of ON ALL (off none) – a llano is a treeless grassy plain
Emphatically not just any part of Athens – it's in Parthenon (3)
I haven't cracked this one yet — but Fifteensquared have:
THE is contained in both aTHEns and parTHEnon and it’s the definite article (emphatically)
Some trouble – but only some – for transport system (5)
Make mad, awfully enraged or otherwise angered (7)
Party vote following piece of text that's contradictory (7)
28a
Writer about chaos goes round the bend – it's a futile quest (4,5,5)
Sharply strike (5)
I haven't cracked this one yet — but Fifteensquared have:
On the surface, this seems like a single definition but a smack can be a sharp sound, as of the lips
See 24
Nonconformist having not even a single way to escape (3.3.3) (9)
Down
Flair seen in Michelangelo's centrepiece (4)
I haven't cracked this one yet — but Fifteensquared have:
Contained in the centre of michELANgelo
North of Land's End, fish moved effortlessly (6)
I haven't cracked this one yet — but Fifteensquared have:
SKATE (fish) + [lan]D
Odd when man changes into this? (4-2-4)
Financial supporters replacing leader with East German socialist (6)
I haven't cracked this one yet — but Fifteensquared have:
[a]NGELS (financial supporters) with the first letter replaced by E (East)
Standard statement of support for barrier (8)
Piece knocked off eg marble counter (4)
One covers two miles in ten, going astray on the way (8)
A name attached? Just the opposite (4)
I haven't cracked this one yet — but Fifteensquared have:
A N (a name) + ON (attached)
After defensive blunder, initially, was captain viewed in inappropriate way? (5)
I haven't cracked this one yet — but Fifteensquared have:
O G (own goal, initially – defensive blunder) + LED (was captain)
What makes Brendan tick, increasing learning (10)
People in America pursue legal redress in hearing (5)
What could be wrong as a rule in a concerning Roman emperor (8)
I haven't cracked this one yet — but Fifteensquared have:
An anagram (what could be wrong) of A RULE IN A: the wordplay suggests an adjective, referring to Marcus Aurelius – but I can’t find this as a definition and there was a less well known emperor Aurelian , so I’m not sure about this
Many notes after poor term, one's performance raised (8)
Sham work without fee turned up (6)
I haven't cracked this one yet — but Fifteensquared have:
A reversal (up, in a down clue) of OP (work) round DUES (fee, as for membership)
Tediously persist, in a word, as monster (6)
It adds fuel to flame in Scottish town (4)
Gloomy tone between chess opponents? (4)
I haven't cracked this one yet — but Fifteensquared have:
GREY is a tone between black and white (chess opponents)
What's flown by a test pilot? (4)
Type letters or click words in the clue