MOO starts off the week…
A very enjoyable start to Monday morning. I'd not come across 27a before.
Thanks MOO!

ACROSS
1. Opposition from Frenchman one intends to marry (8)
DEFIANCE
DE (from, French) + FIANCE (man one intends to marry)
5. A writer capturing painter’s language (6)
ARABIC
(A + BIC (writer)) capturing RA (painter)
10. Purity of gold providing an inducement, might one say? (5)
CARAT
"carrot" = CARAT (an inducement, "might one say")
11. Unhappy Days — the memoir of a setter? (1,4,4)
A DOGS LIFE
Double (cryptic) definition
12. Scandalmonger’s friend concealing old boat capsizing (9)
MUCKRAKER
MUCKER (friend) concealing (ARK)< (old boat, <capsizing)
13. As a joke, starts to flaunt underwear in boozer (2,3)
INFUN
(F[launt] U[nderwear] (starts to)) in INN (boozer)
14. A sign of global warming? That’s baloney (3,3)
HOT AIR
Double (cryptic) definition
15. Academic haunted by endless longing in prison cell (7)
DUNGEON
DON (academic) haunted by [h]UNGE[r] (longing, endless)
18. This timeless writer’s a self-important chap (3,4)
HIS NIBS
[t]HIS (T(time) less) + NIBS (writer's)
20. Unfriendly cook harbouring east German (6)
FROSTY
FRY (cook) harbouring OST (east, German)
22. A spread for Mrs Simpson? (5)
MARGE
24. After being rejected I had to hit back (9)
RETALIATE
(LATER)< (after, <being rejected) + I + ATE (had)
25. Predator giving old Cicero a shock (9)
CROCODILE
(OLD CICERO)* (*given a shock)
26. Son out of line? Rubbish! (5)
TRIPE
[s]TRIPE (line, S (son) out)
27. Camp American drinking beer? On the contrary (6)
LAAGER
LAGER (beer) drinking A (American)
28. Supporter died in Teheran unfortunately (8)
ADHERENT
D (died) in (TEHERAN)* (*unfortunately)
DOWN
1. Leave city in the rain (6)
DECAMP
EC (city, postcode) in DAMP (the rain)
2. Cruel? Of course I can become so (9)
FEROCIOUS
(OF COURSE I)* (*can become so)
3. Electoral system producing veto? (11,4)
ALTERNATIVE VOTE
(VOTE)* (*alternative) = VETO
4. Attractive girl but almost completely mad (7)
CRACKER
CRACKER[s] (mad, almost completely)
6. Mad gamble with Rasputin maybe leading way round obstacle (7,8)
RUSSIAN ROULETTE
RUSSIAN (Rasputin maybe) leading ROUTE (way) round LET (obstacle)
7. A run-down lawyer (5)
BRIEF
8. Tory tendency to create low-wage work? (8)
CLEANING
C (Tory) + LEANING (tendency)
9. According to reporters, weapon went through roof (6)
SOARED
"sword" = SOARED (weapon, "according to reporters")
16. Taxi meter running beyond 90 minutes? (5,4)
EXTRA TIME
17. Helium replacing oxygen in funny kind of reaction (8)
CHEMICAL
COMICAL (funny), HE (helium) replacing O (oxygen)
19. Broadcaster’s honest sound (6)
STRAIT
"straight" = STRAIT (honest, "broadcaster's")
20. F for fool (7)
FATHEAD
21. Moderate torn about Robespierre’s revolutionary article (6)
RELENT
RENT (torn) about (LE)< (Robespierre's article, <revolutionary – not that it matters)
23. Wine and port getting nod from Benedict XVI? (5)
RIOJA
RIO (port) getting JA (nod from Benedict XVI – being German)
A steady solve from Moo here, with lots of interesting devices (which I’m noting for blogging).
Thank you to Teacow and Moo.
A very nice start to the week. LAAGER rang a faint bell but was also the only sensible option in the end!
Thanks Moo and Teacow.
I couldn’t think of an endless longing in 15a. Was puzzled by let/obstacle (tennis?). And I’ve never heard of mucker/friend — Collins says it’s British slang. LAAGER was new to me.
All else was hunky dory and good fun. Thanks Moo & Teacow.
Mucker I remember from Neville Shute and thought it was Australian (I’m sure it’s in A Town Like Alice – said by the Australian protagonist) – he was writing in the 1950s.
Let is tennis – serving hitting the net gives a let.
I was aware of LAAGER and associate it with the Boer War. On checking Chambers, I see it is a defensive formation of ox-wagons – the veldt equivalent of the Wild West circling of wagons, I guess. From which developed its use to mean a defensive position.
GDU – let is almost exclusively thought of in the tennis context but it also lives on the in the phrase ‘without let or hindrance’, simply meaning ‘without obstruction’. Used in connection with right to vote and/or crossing international borders. However, let on its own to mean obstruction, other than in tennis, is noted as archaic.
SWORD, CHEMICAL and CROCODILE, my faves today. Thanks Moo and Teacow.
I second Amoeba @2. It took me some time to parse “Arabic” as the royal academician somehow evaded me! Thanks for the fun Moo and the elucidation Teacow.
Liked the Playtex of “French man” in 1a DEFIANCE.
And the two “writer”s in 5a ARABIC and 18a HIS NIBS.
And all the lovely surfaces.
Thanks M&T.
Very enjoyable as Teacow says and nothing that was excessively obscure but I do worry that the use by setters of such old fashioned phrases as 18ac wil do nothing to attract a new generation to the world of the cryptic
Thanks, Shanne & PostMark.
Still baffled by FATHEAD, ironically.
Tank, F is the head of “fat”.
I was a bit tired when I did this, and found it quite difficult in places. I was unable to spot the same words as GDU@3 and I was not aware of ALTERNATIVE VOTE either.
Thanks Moo and Teacow
Oh dear. I am old fashioned as I use both “HIS NIBS” and mucker from time to time.
Quite a straightforward puzzle which. I much enjoyed.
Thank you Moo and Teacow .
Thanks for the blog, good range of neat clues and I like the old words and phrases.
Not sure about EXTRA TIME , a water polo match only lasts for 32 minutes , so why 90 ?
Roz@14. Much as you might deplore it, 90 minutes refers to (association) football. At least the FT doesn’t give us football references too often.
Thanks to Moo for the puzzle and Teacow for the blog.
What’s more, there is no extra time in international water polo. Matches go straight to a shoot out. ):
I thought this was fun. ALTERNATIVE VOTE was my favourite, as I so often miss these reverse clues.
For nearly all levels of water polo there is extra time , multiple periods if needed , I would prefer the setter to use this instead of the diving competition.
Got nearly there. Didn’t know but parsed alternative. Didn’t know mucker but guessed muckraker. Never heard of his nibs and left that empty. But great fun all round! I know I’m many hours behind most of you. I have no idea if anyone reads my late post therefore. But thank you all again!
AS@19 – I read it!
I liked this. Very enjoyable. “Laager” was new, but only few problems overall. Thank you to Moo and thanks to Teacow, especially for parsing “Muckraker” and “Dungeon”
Got to this the following day and enjoyed enormously. I thought there were some really wonderful clues. I have certainly heard of Laager. Funny, isn’t it how one is surprised sometimes how words you don’t think of as unusual are unknown to other solvers, but then of course the reverse occurs…..
Thanks Martyn!