Across:
8 Heartless (without centre/middle = ‘r’) in Endeavour (try) (‘try’ without ‘r’ = TY-), the lead in Porridge (the lead in ‘Porridge’ = -P-) and the original (the ‘first’ = 1ST = -IST) (TYPIST) key contributor to The Office (TYPIST),
9 Vindication (APOLOGIA) for a (A-) flower (flower/river Po = -PO-) on part of the tree (-LOG-) leads to internal analysis (leads to ‘Internal Analysis’ = -IA) (APOLOGIA),
10 Don’t resist (OBEY) somebody kicking out the Mods (‘somebody’ kicking out the ‘mods’ = eboy = OBEY),
11 Fair amount of (half of) the check-up (half of ‘EXam’ = EX-) is needing attention (is -PRESSING) (EXPRESSING), in a manner of speaking (EXPRESSING),
12 Bloodthirsty parasite (BEDBUG) has what the spies use to listen in on honey trap perhaps (BEDBUG),
14 Uneven (LOPSIDED), confusing (= anagram indicator), odd piles (odd piles = LOPSIDED),
15 Secretary (SHORTHAND TYPIST) to most of (s) those in 26 across (‘shorts’ without ‘s’ = SHORT-), 24 across (‘hand’ = -HAND) and 8 across (‘typist’ = TYPIST) (SHORTHAND TYPIST),
18 Jersey (TAX HAVEN) and casual shirt (T- shirt) is for a (-A-) mystery man (Mr - X) from shelter (HAVEN) (TAX HAVEN),
20 Accounting jobs (AUDITS) they don’t have in 18 across presumably (they don’t have AUDITS in ‘tax haven’),
22 You can get this if you really try (OBTAINABLE) to secure (OBTAIN-) a (-A-) barrister (-BL-) from England (-E) (OBTAINABLE),
24 Hook (HAND) and Sutherland dismiss result (‘Sutherland’ dismiss ‘result’ = hand = HAND),
25 Wild (= anagram indicator) kale is no (kale is no = SNAKE OIL) good for those who want a silly panacea (SNAKE OIL),
26 It would be obscene to not have them for the team photographs (SHORTS) or films (SHORTS).
Down:
1 So long (so long! = BYE-BYE) as you hear this (= homophone indicator) repeatedly during a bull market? (bull market/share prices are up, so ‘buy-buy’ = ‘BYE-BYE’),
2 It can be associated with The Centre (CITY centre) bordering the suburbs (CITY),
3 Rents (rents = STREN-) complex (= anagram indicator) from Government (-G-) with most of (e) the (‘the’ without ‘e’ = -TH) (STRENGTH) power (STRENGTH),
4 1000 (-M-) involved in strike (strike/hit = RA-P) (RAMP) coming off The Hill (RAMP),
5 Came alive (WOKE) at a wake (awake = UP) (WOKE UP) and began to face reality (WOKE UP),
6 Turned up (= reversal indicator) to join the crew (row = WOR-) on the Titanic? (SHIP-) Initially poor (initially ‘Poor’ = -P-) writer (-ED) (WORSHIPPED) put on a pedestal! (WORSHIPPED),
7 Drugs (-EE-) in prison (prison = PION-RS) produced by (= anagram indicator) (PIONEERS) those who are unaffected by the bars presumably (those who don’t drink = PIONEERS),
13 Deliveries (births = BIRTH-S) around old capital (old capital/money = -MARK-) (BIRTHMARKS)– the types that leave impressions on you for life (BIRTHMARKS),
14 Some individual in England (some ‘individuaL IN ENgland’ = l in en = LINEN) is hung out to dry (LINEN),
16 Senior type (HEAD-) from Bar (bar/prohibit = -BAN-) finds 500 (Roman 500 = -D) (HEADBAND) in court attire? (HEADBAND on tennis court),
17 Pass through (TRAVERSE) vet’s rare (vets rare = TRAVERSE) building (= anagram indicator),
19 The one trading (VENDOR) by meandering (= anagram indicator) Devon (Devon = VENDO-) river (-R) (VENDOR),
21 Principals (‘principals’ = ‘principles’ = TENETS), say (= homophone indicator), with beliefs (TENETS),
23 Gets a kicking (BALL) for having no ties to Bastille (having no ‘ties’ to ‘Bastille’ = ball = BALL),
24 Local belt (belt/punch = HOOK) taken by boxer perhaps (HOOK).