Independent on Sunday 1097 by Quixote

As to be expected, The Don served up another scrupulously fair puzzle that can be enjoyed without too much problems on a lazy Sunday.

ACROSS
1 CERISE Ins of ERIS (rev of SIRE, father) in CE (Church of England)
4 ASPIRANT *(PARTISAN)
10 SUPERHERO SUP (drink) + ins of HE in ERROR (mistake) minus R
11 GROVE GROVEL (crawl) minus L
12 ONION Ins of I (one) in ON ON (functioning repeatedly)
13 REPROBATE Ins of PRO (professional) in REBATE (money back)
14 BABY GRAND PIANO *(a bad granny I bop)
17 UNDERSTATEMENT Cha of UNDER (dictated to) STATE (body politic) MEN (chaps) T (time)
21 PARTY LINE dd
23 CRIME C (cold) RIME (frost)
24 EASEL EASE (calm) L (lake)
25 KNOW-IT-ALL Cha of K (king) NO WIT (humorous person) ALL (everyone)
26 ANNOYING ANN (girl) BOY minus B (boy beheaded) I (one) NG (no good)
27 BETTER dd

DOWN
1 CUSTOM CU (copper)+ *(most(
2 REPRIMAND REP (representative or salesman) + ins of I’M (I am) in RAND (money abroad in S.Africa)
3 STRINGY Ins of R (river) in STINGY (mean)
5 STOPPING THE ROT *(nightspot toper)
6 IN-GROUP *(grin) + OUP (Oxford University Press)
7 AROMA A ROMA (Rome as the Italians call it)
8 THEREFOR THE REFORM (change) minus M
9 TERROR-STRICKEN *(RK stern rector I)
15 ANNUITANT Formulaic cha of ANN (girl) U (university) IT ANT (hard worker)
16 SUBPOENA *(bean soup)
18 ROYALTY Income that may come when a certain volume’s sold (7)When I solved this from crossing letters, I looked hard to find the wordplay only to discover that this is a poor cd (no aha! effect). Income for Elizabeth’s family or even Family in Windsor would have made credible dd and cd.
19 MACHINE MACH (speed of sound) I (one) NE (one minus O, nothing)
20 SELLER Ins of LL (two pounds) in SEER (wise man)
22 RESIN Tichy was to say SIN (go wrong) again

Key to abbreviations
dd = double definition
dud = duplicate definition
tichy = tongue-in-cheek type
cd = cryptic definition
rev = reversed or reversal
ins = insertion
cha = charade
ha = hidden answer
*(fodder) = anagram