A very good puzzle.
The only downside of a puzzle like this is that it being essentially perfectly constructed there is nothing left for me to comment on. Thank you Poins.

| Across | ||
| 1 | REPAST | Start to regret taking ecstasy after a meal (6) Regret (starting letter of) with E (ecstasy) PAST (after) | 
| 4 | BELIEF | Fail to give a true impression of Frederick at the beginning of Persuasion (6) BELIE (fail to give a true impression of) F (beginning of Frederick) | 
| 8 | EVICTED | Put out directive ignoring Irish revolutionary (7) DirECTIVE* anagram=revolutionary | 
| 9 | PIT PONY | A matter for regret admitting pressure on mineworker (3,4) PITY (a matter for regret) including (admitting) P (pressure) ON | 
| 11 | ILLUSTRATE | Explain with pictures of the Italian soldiers returning in splendour (10) IL (the, Italian) with TA (Territorial Army, soldiers) reversed (returning) in LUSTRE (splendour) | 
| 12 | SAYS | Soldiers guarding the earliest of Yankee states (4) SAS (soldiers) containing (guarding) Yankees (first letter, the earliest letter of) | 
| 13 | GREEN | Fresh information involving queen from the east (5) GEN (information) containing ER (The Queen) reversed (from the east, reading right to left on a map) | 
| 14 | TAPESTRY | Attempt to capture saint standing by animal in ornamental textile (8) TRY (attempt) contains (to capture) ST (saint) following (standing by) APE (animal) | 
| 16 | LINGERIE | Row over Ms Halliwell’s underwear (8) LINE (row) containing (over) GERI (Ms Halliwell, of the Spice Girls) | 
| 18 | RANGE | Take sides with soldier for the most part (5) RANGEr (soldier) mostly | 
| 20 | PAIN | American horse’s endless suffering (4) PAINt (a piebald horse in America) missing the end letter | 
| 21 | DISCONCERT | Upset to find candlestick covered with muck (10) SCONCE (candlestick) inside (covered with) DIRT (muck) | 
| 23 | GODSEND | The intention of Apollo for example revealed by a stroke of luck (7) GOD’S END is the END (intention) of a GOD (Apollo for example) | 
| 24 | HAVE A GO | Try to grasp the point of American board game (4,1,2) HAVE (to grasp the point of) A (American) GO (board game) | 
| 25 | ENSURE | Guarantee heading off reprimand (6) cENSURE (reprimand) missing head (first letter) | 
| 26 | BEDSIT | Son breaks new bidet in rented accommodation (6) S (son) inside (breaks) BIDET* anagram=new | 
| Down | ||
| 1 | REVEL | Take great pleasure in continually going over to Luxembourg (5) EVER (continually) reversed (going over) to L (Luxembourg) | 
| 2 | PICTURE | Call to mind a bit of advice about crossing Cambodia’s principal river (7) TIP (a bit of advice) reversed about containing (crossing) Cambodia (principle, first letter of) then URE (a river) | 
| 3 | SWEETENER | Resent failing to receive small backhander (9) RESENT* anagram=failing containing WEE (small) | 
| 5 | EXILE | Banishment of former priest is overturned (5) EX (former) ELI (priest) reversed (is overturned) | 
| 6 | IMPOSTS | Minister’s first job? To cut Iceland’s taxes (7) Minister (first letter of) POST (job) inside (to cut) IS (Iceland, IVR) | 
| 7 | FANCY-FREE | Not currently in love like Frank (5-4) FANCY (like) and FREE (frank) | 
| 10 | PANTHEIST | Spinoza was one of the first to be seen after blast (9) THE IST (the 1st) following PAN (blast, criticise) | 
| 13 | GO IT ALONE | Talk at length about Italian gangster having energy to act without help (2,2,5) GO ON (talk at length) containing (about) IT (Italian) AL (Al Capone, gangster) then E (energy) | 
| 15 | PERFORATE | Fellow salesman standing up to make a speech can be seen in Punch (9) F (fellow) REP (salesman) reversed (standing up) then ORATE (to make a speech) | 
| 17 | GENESIS | Book showing a form of gneiss seen around Spain (7) GNEISS* anagram=’a form of’ containing E (Espana, Spain) | 
| 19 | NICKERS | Sniggers as dubiously stricken opponent finally quits (7) StRICKEN* anagram=dubiously missing opponenT (final letter of) | 
| 21 | DONOR | Act on denial by Republican benefactor (5) DO (act) on NO (denial) by R (republican) | 
| 22 | RIGHT | Appropriate for an associate of Cobden to reject hint of bias (5) John bRIGHT (associate of Richaed Cobden) missing Bias (first letter, hint of) | 
definitions are underlined
I was doubtful about equating “sniggers” with “nickers”, but that seems to be the answer. While I’ve a dim memory of Cobden, I don’t recall his association with Bright, but that didn’t stop me writing in the answer. All fine stuff and not too much exertion for a Sunday morning! PeeDee and Poins, thanks very much.
I found this one trickier than a lot of IoS puzzles and I class it as a good mental workout. It took me a while to see GODSEND, I didn’t know Spinoza was a PANTHEIST and had to rely on the wordplay, and I struggled with several in the NE quadrant, namely BELIEF, PIT PONY, FANCY-FREE and IMPOSTS. RANGE was my LOI after I decided that there wasn’t a valid alternative.
Good puzzle, maybe a bit harder than your usual Poins.
I’d always thought NICKER meant ‘whinny’ or ‘neigh’. I’ve never associated it with ‘snigger’.
Thanks to S&B.
According to my Chambers there are several meanings of NICKER. Two of them are a verb meaning to snigger, and a noun meaning a snigger or a loud laugh. It adds that they are chiefly Scottish and Northern English. That said, I usually associate the word with horse sounds or pound coins. A couple of the more obscure meanings of the word are a water monster or water demon, a clay marble, and the round seed of a Caesalpinia or Guilandina used for playing marbles.
Two “equine” clues to comment on: I didn’t know PAIN(t) as a piebald horse; and I liked the slight misdirection for PIT PONY in that I didn’t at first think of a non-human worker.
But all very sound and well-constructed.
Thanks, Poins and PeeDee
I had some doubts about the accuracy of various definitions while solving this puzzle. As I had a whole week to write up the blog I started looking them all up in Chambers. In every single case Poins was spot on, usually quoting the definition verbatim from the dictionary. After a while, probably being perverse, or maybe just not having anything better to do, I looked up all manner of words used anywhere in the puzzle. In the end I couldn’t find a single word that didn’t have a sound, usually verbatim definition.