I found this a very unusual crossword, much tougher than usual (perhaps scheduled because of the Bank Holiday).    I spent 47 mins at it, but did not solve it, not getting 23 ac

* = anagram  < = reversed

ACROSS

1 NA (POLE  O)  N

6 A S WELL

9 BETEL GE (’extremely gruesome’ = first and last letters)  USE

10 Dead as a DO DO

11 C (LE (AVA)G) E     Actress Ava Gardner from quite a while back.

13 BARRA (ge)

14 SORDID   hidden

15 LOCKS (secures) TEP   Pet<

17 G (Glow-worm’s beginning) EODESIC    (codes ie)*, I think

19 NELLIE    Got this right without knowing why   “When she married a cleric, she used to sit and dream”   Refers to something this blogger ain’t come across.

20 THE ME

22 IN WARD L(il)Y

23 LIME     “Soil treatment for one of two trees”     Had to look this up and do not understand it.

24 SUI GENERIS    (ruins siege)*

26 HECTOR   H for R in Rector    R is third letter of parishioners.

27 EX TOLLED

DOWN

2 AVE  (abbrev for avenue)

3 ONE-HANDED

4 ENGLAND  N (last of salmon) in (angled)*

5 NOUVELLE CUISINE     If I’ve interpreted this correctly it’s (Nice U lovelies un)* with undressing splitting into un dressing and dressing indicating the anagram.      Well Eimi’s said he not always strictly Ximenean…

6 ALE (MBI) C     Alec Guinness, actor

7 WADER   Hidden <

8 LUDGATE HILL    (A dull light)* containing E

12 LOOS EST RIFE

16 S (OLAR C) ELL    (coral)*

16 S (one of several) PENS ER

19 NE W LEFT

21 EVE N T    noontime = nt   More non-Xim splitting, I think.

25 IKE   Alternate letters  Nickname of President Eisenhower