A well-balanced, but not too daunting puzzle. Just what the Doctor ordered for the morning-after-the-office-party, in my case.

Across
1 UN,OBTR(U)SI,VE(-t) - Phew, glad we got that three-line, thirteen word clue out of the way at the first time of asking.
10 CRIM(PL)E,NE - I’m never quite sure whether “Tyneside”=NE is referring to the Newcastle postcode or just the North-East in general….
12 O(TAG)O - is the region. Do the Kiwis call them states, like the Ozzies?
13 R(HEN,IS)H - I suspect that there is a less clunky alternative to “outskirts of Redditch” to denote RH.
24 REALITY TV (Let it vary)*
26 S(ART)ORIAL - (sailor)*. Took me longer to figure out the wordplay than the answer.

Down
1 UPSTAIRS - double def, and a good’un to boot.
2 OLD TIMER - “Hunter” is/was a type of watch.
4 UN,C(OUT)H
7 P,RE,FAB
8 BR,ETON - An original, cross-Channel usage of “Celt”. I instinctively started working through Irish/Scottish terms.
16 CITY(DE)SK - Ed(rev) in (Sticky)*
19 M(A,RM)ITE - “jolly”=Royal Marine. Factoid Alert: I believe that Marmite is actually named after the French word for the type of jar that it comes in.
20 SN(A,R(L)U)P - Kudos for creating a double container/contents clue with only six words!
22 D(V)O,RAK(-e) - but I suppose the crossing letters _V_R_K are something of a giveaway.

I’m a bit short of time today so this will be a less detailed than usual entry. Apologies in advance etc…

Across
1 LITTLE TOE - I put in LITTLE PIG at first, which didn’t help with 4 and 5 down, the last two I got!
11 DE(PORT)MENT - “Make nuts” is a great def for DEMENT.
12 SEMI - (t)IMES reversed.
17 AND/OR,R.A. - pretty clever, assuming that the / on its own really does mean and/or.
22 PA(RAP)LE,GI,C
25 NINETIETH - “top of the house” being 90, the highest number in bingo.

Down
1 L(UC)ID - UC = upper case, i.e. cap(ital)s.
2 T(RUM,PC)ARD - “up bother” = DRAT reversed.
4 TOTEMIC - (Oct time)*
8 DI(S-SIDE)NT - I’m not keen on clues that use stuttering in the wordplay. Just strikes me as lazy, even though the worst offenders are probably Azed and Araucaria!
14 FLAGRANCE - change the first R of FRAGRANCE to L.
21 FE(N,C)E
23 CONCH(i.e.) - conchie is slang for a conscientious objector.

I’d read four or five clues before I realised that something odd was going on and at first I thought the wrong grid had been printed. Then I spotted that there was no Across or Down, just “Clues”. And it was only when I’d completed the grid that I saw the Nina: the unchecked letters in the top row and along the bottom (starting from the 25 square) spell out ADVENT CALENDAR. I’m guessing it wasn’t possible to create a workable grid that had 25 entries as that would have replicated an advent calendar exactly - one clue per door.

Solving time: 10 minutes when I gave up …

… trying to work out 6D. I don’t know quite enough gods and ?A?A?A?A doesn’t help much. I guess the story is a SAGA, the Hindu god could be RAMA, and the Egyptian one could be RA, but that’s too much material it seems. So after searching a couple of god lists in vain, I surrender and wait for the name of the unknown god, or the revelation that I’ve completely misunderstood the clue. “Nice easy Phi”, thought I when I saw that this blogging slot was free. Serves me right! Part of the problem may be what an old Times champs rival of mine calls “vocalophobia” - a fear of vowels as the only checking letters, especially repeated common vowels.

And later on it turns out I got another carelessly wrong - 14D.