Across:
8 Grace O’Malley (PIRATE) works presumably on the Crime Wave overseas (PIRATE),
9 Check your lines in advance (REHEARSE) for catches (-HEARS-) in lough (Lough RE-E) (REHEARSE),
10 Swelter (BAKE) on the outskirts of Basingstoke (on the outskirts of ‘Basingstoke’ = BAKE),
11 The hatchet man (WOODCUTTER) brought in to the cut the dead wood out of Nottingham Forest (WOODCUTTER),
12 It (I-T) includes Mike (-M-) from Cork (cork/cap = -PAC-) retiring (= reversal indicator) (IMPACT) from the force (IMPACT),
14 One gives up the ghost (EXORCISM) by emptying the spirits (EXORCISM),
15 Gallery type (PICTURE) gets letters (POST-) for Christmas (Christmas card = -CARD) (PICTURE POSTCARD) – it’s what you’d expect during the holiday season (PICTURE POSTCARD),
18 Leaves home (home of the tea leaves = TEA CADDY) to be a mentor (teach) briefly (h) (‘teach’ without ‘h’ = TEA C-) to family figure (daddy) starting off (d) (‘daddy’ without ‘d’ = -ADDY) (TEA CADDY),
20 Holy cow! (OH DEAR!) Head Office (HO = OH) goes back (= reversal indicator) on word to open letter (DEAR ...) (OH DEAR),
22 Roughing it (CAMPING) on holiday (OUT) (CAMPING OUT) looking up at the stars (CAMPING OUT),
24 Rock- (SWAY) -and-roll? (SWAY),
25 On the radio (= homophone indicator) Jim (‘Jim’ = ‘gym’ = PE-) Power (-P) spills the beans (TALKS) (PEP TALKS) with motivational speeches (PEP TALKS),
26 New (= anagram indicator) cigar (cigar = GAR-IC) filling left (-L-) (GARLIC) a pungent aroma on the breath (GARLIC).
Down:
1 Take the sting out of the tail (DISARM) with charm (charm/beguile = DISARM),
2 Holds the beer (CASE of beer) bottle for Monica Seles (bottle for ‘Monica Seles’ = CASE),
3 One member of overseas Special Forces (SEAL) nearly (l) (‘seal’ without ‘l’ = SEA-) gets drunk at The Tap (WATER) (SEAWATER) – it holds the ship up! (SEAWATER),
4 The Verve (verve/gusto = BRIO) in Brazilian capital (‘Brazilian’ capital = B-) city in South America? (-RIO) (BRIO),
5 Women (W-) saw (saw/cut = -HACK-) duck (-O) (WHACKO) with local cuckoo (WHACKO),
6 The foreign (the = LA-) college (-C-) upsets (= reversal indicator) most of (y) The City (‘city’ without ‘y’ = cit = -TIC) – it’s corrosive stuff (ACID) (LACTIC ACID) that leaves a sour taste (LACTIC ACID),
7 Make up one’s mind about (ASSESS-) old (-O-) writing (from the 3Rs = -R) (ASSESSOR) in The Examiner (the examiner = ASSESSOR),
13 Be prepared for (ANTICIPATE) madcap (ANTIC-) Irishman (-PAT-) in Ireland (Ireland domain = .ie = -I-E) (ANTICIPATE),
14 Stop payment – without pantos (‘stop payment’ – without ‘pantos’ = tpyme = EMPTY) this would be meaningless (EMPTY),
16 Make rice (make rice = ICE MAKER) dish (= anagram indicator) and keep it in the freezer (ICE MAKER),
17 It’s not enough (SHORTAGE) to organise (= anagram indicator) her goats (her goats = SHORTAGE),
19 Note (music note D-) relates to local fireplace (-INGLE) (DINGLE) found in the kingdom (DINGLE in The Kingdom / Kerry),
21 Bill (AD-) is at the bar (Attorney General = -AG-) before ten (10 = -IO) (ADAGIO) – that’s slow for a musician (ADAGIO),
23 Put out (OUST) sample of the langoustines (sample of the ‘langoustines’ = OUST),
24 Guess who’s leaving Burgesses’ (‘guess’ who’s leaving ‘Burgesses’ = bres = SERB) Croatian neighbour? (SERB).