Guardian 24274/Paul – fish or fowl?

Neither fish nor fowl — can’t tell if there’s really a theme here or not: do fish and chips and grouse and chickens and pecking qualify? A couple of wordplays that I’m still struggling with… sometimes I manage to work them out as I write up my notes. If not… please have at them. Updates from comments below…

Across

1	GR[eat],OUSE – it’s a bird and OUSE is a river but “eat from”? “Eat from river, as bird”. The river is GREAT OUSE from which “eat” is removed.
4	PA(RAF,F[og])IN – the RAF are collectively “airmen”. Good example of seeing the answer before I worked out the wordplay.
9	[e]NO,U,GAT – rev(tag=name, u, on[e]) where U=upper-class I suppose for “posh”
11	I DON’T MIND IF I DO – def is an idiom for “thanks” but wordplay? “So my resentment is not to be trusted? Thanks!” See Geoff’s interpretation below.
13	CHIC=smart,KEN,P,OX=steer – def is just the very nicely hidden “spots” with KEN starring as our “boy”.
18	IMPECCABLE=”impeckable” – Paul indicates that this isn’t really a word with the question-mark.
21	WIND RESISTANCE – (in car witnessed)*: your ability to withstand a blast (of air) would be your WIND RESISTANCE rating.
24, 17	FR(YING TON[g])IGHT – I guess the chip shop’s proprietor is back from his fishing trip. I actually recognized the Goon’s “Ying-Tong song” — which just goes to show what kind of education I received at home from my father.
25	NOT,A,T[h]ING – “BeetHoven’s fifth” is invariably H – and in this case, “love” is NOT A THING rather than NOTHING. Consensus is that it’s actually NOT [h]ATING, since love is the absence of hate presumably.

Down

1, 7	GONE FISHING – (sign of hinge)* – good surface with apposite fodder for the fish and chips shop surface.
2	OPUS DEI – (Oedipus)* — read “The Davinci Code” recently which helped.
3	S(EA SN)AKE – somewhat unusual wordplay: a hidden string inside of a container, where EASN is hidden in: “observE AS Natural” all inside SAKE our “drink”
6	ARM,PIT – Paul reveals that he doesn’t shave nor wax his armpits.
12	MAN,U,MISSION – not an everyday word for emancipation, MAN U’s our football team.
13	CHAR,W,OMAN – CHAR’s our fish and OMAN’s our nation.
15	I(C(E) AP)RON – double containment: it’s a “wedge-shaped structure which protects a bridge pier from floating ice” and IRON’s our metal.
19	BACKING – my fav, very Paulian, clue since troppus is BACKING(support).
22	EGGY – is this anything more than a cryptic definition? “Dressed in yellow and white?”