Across:
1 Blows (= anagram indicator) nose (nose = SE-ON) outside address (Mr), upset (= reverse indicator) Mr = -RM-) (SERMON) with what amounts to a preaching (SERMON),
4 Fog coming off golf courses (‘fog’ coming off ‘golf courses’ = lcourses = CLOSURES) leads to stoppages (CLOSURES),
9 Cider producers (APPLES) in 21 across (‘apple’ = APPLE-) on bender (-S bend) (APPLES),
10 The roots (HERITAGE) of one (-I-) child’s game (-TAG-) wrapped up in the present (HER-E) (HERITAGE),
12 Spike (PIN-), Earl (-E-) and Dick Davies, for example (“Dick Davies” is the name of Irish Heritage apple = -APPLE) (PINEAPPLE) – one of which produces tropical fruit? (PINEAPPLE),
13 Passage (INLET) from sample of chain letters (sample of ‘chaIN LETters’ = INLET),
14 Ill-mannered (DISCOURTEOUS) detective (Detective Sergeant = D-S-) imprisons one (-I-) polite type (-COURTEOUS) (DISCOURTEOUS),
18 Gathering intelligence around the earth (SPY SATELLITE) for a gent (‘a gent’ = ‘agent’ = SPY) going to The Moon (The Moon is a natural SATELLITE of the earth) (SPY SATELLITE),
21 Irish Peach (“Irish Peach” is the name of Irish Heritage apple = APPLE) found mostly in 9 across (mostly ‘apples’ = APPLE),
22 Countrymen (RURALISTS) on top of Rocky (on top of ‘Rocky’ = R-) Mountains (Urals = -URAL-S) over Christmas from The Centre (‘chrISTmas’ from the centre = -IST) (RURALISTS),
24 Old metal containers (CRESSETS) of salad (CRESS-) from propagated young cuttings (sets) that need no introduction (s) (‘sets’ without ‘s’ = -ETS) (CRESSETS),
25 Most (s) of those in 19 down (sauces) (‘sauces’ without ‘s’ = SAUCE-) writing (from the 3Rs = -R) (SAUCER) to supporter of The Cup (SAUCER),
26 Those going for a walk (STRIDERS) to pick up (= reverse indicator) malicious gossip (dirt = -TRID-) on English (-E-) ringleader (‘Ring’ leader = -R-) in ship (SS = S-S) (STRIDERS),
27 Made fun of (TEASED) sedate (sedate) drunk (= anagram indicator) (sedate = TEASED).
Down:
1 Charge (STAMPEDE) for squash (STAMP-) yield (cede) starting off (c) (‘cede’ without ‘c’ = -EDE) (STAMPEDE),
2 Maturity (RIPENESS) of peers in (peers in = RIPENES-) foreign (= anagram indicator) society (-S) (RIPENESS),
3 Switches (= reversal indicator) a (-A) precious stone (gem = -MEG-) for ring (O-) (OMEGA) – the last in a series (the last letter of Greek alphabet = OMEGA),
5 The make-up artists set them off presumably (LIE DETECTORS), as they recognise a good yarn when they hear it (LIE DETECTORS),
6 Religious (SPIRITUAL) Greek character (16th letter of the Greek alphabet = -PI-) behind (= position indicator) school (S-) practice that’s regular (-RITUAL) (SPIRITUAL),
7 Without a doubt (REALLY), it’s a meeting (R-ALLY) about drugs (ecstasy = -E-) (REALLY),
8 Small (S-) bits of purses (-CENTS) (SCENTS) picked up by boxers (dogs) (SCENTS),
11 One of those in the media talking about the club (SPORTSWRITER) – the one reporting the fights (SPORTSWRITER),
15 Persecuted (OPPRESSED) old (O-) soft (soft/piano = -P-) media (-PRESS-) writer (-ED) (OPPRESSED),
16 Analyses (DISSECTS) record (disc) cut (c) (‘disc’ without ‘c’ = DIS-) by offshoots of group (-SECTS) (DISSECTS),
17 Poured a glass (MEASURED) to assess (MEASURE-) the last of the blend (the last of the ‘blenD’ = -D) (MEASURED),
19 Lots missing from Cassoulets (‘lots’ missing from ‘Cassoulets’ = cassue = SAUCES), Hollandaise and Béchamel, for example (SAUCES),
20 Emerge (APPEAR) with a (A-) starter of passion (starter of ‘Passion’ = -P-) fruit (-PEAR) (APPEAR),
23 Go on holiday (LEAVE) to Split (LEAVE).