Across:
8 One of many by Vivaldi (SONATA) produced wince from Isaac Newton (‘wince’ from ‘Isaac Newton’ = saanto = SONATA),
9 One (I-) atlas in (atlas in) production (= anagram indicator) (atlas in = -TALIANS) (ITALIANS) for the French neighbours (ITALIANS),
10 Some job at hotel (some ‘joB AT Hotel’ = BATH) in English city (BATH),
11 Characters in 1 down (‘Romans’ = ROMAN -S) hiding 10 across (‘Bath’ = BATH-) (ROMAN BATHS) in old places where some wanted to get clean (ROMAN BATHS),
12 Throwaway lines (ASIDES) from The Undertones on stage (ASIDES),
14 Two types of workers (hand + man = HAND-MAN) around yard (-Y-) (HANDYMAN) – one is a jack-of-all-trades (HANDYMAN),
15 Turns up (= reverse indicator) Heath (moor = ROOM) has fever (TEMPERATURE) (ROOM TEMPERATURE) – one tends to get that when all the windows are closed in The House (ROOM TEMPERATURE),
18 Port (P-) ain’t (-AINT) on River (River PO-) Thames? Primarily (‘Thames’ Primarily = -T) (PAINT POT), it’s the one used by Constable, for example! (PAINT POT),
20 Lead batteries (lead ‘Batteries’ = B-) found in crumbly soil consisting of clay and lime (marl – MAR-L-) on the ultimate (the ‘ultimatE’ = -E) (MARBLE) hard rock (MARBLE),
22 US prices on (US prices on) foreign (= anagram indicator) (US prices on = PERCUSSION) drums (PERCUSSION),
24 Surgeon discharges one (‘surgeon’ discharges ‘one’ = surg = RUGS) of the runners (RUGS),
25 State support (MAINTAIN) for chief (MAIN-) and Troy (-T-) leaders – Achilles, Idomeneus, Nestor (leaders ‘Achilles Idomeneus Nestor’ = -AIN) (MAINTAIN),
26 Motorway (-MI-) divides Lough (Lough ER-NE) (ERMINE) in Royal Trim (regal/ceremonial trim on garments = ERMINE / white stoat fur),
Down:
1 One of the good books (ROMANS Book of New Testament) scattered around the Vatican (ROMANS),
2 Whip (LASH) is the Spanish (‘the’ Spanish = LAS-) leader of The House (leader of the ‘House’ = -H) (LASH),
3 A (-A-) mark (-CROSS-) in the foreign (le = L-E) (LACROSSE) game (LACROSSE),
4 First mate has no taste (‘first mate’ has no ‘taste’ = firm = FIRM) for company (FIRM),
5 A general rule (canon = CAN-ON) covering new (-N-) (CANNON) equipment produced by a major employer (CANNON),
6 Relates to two (BINARY) informers (rats) giving up (= reverse indicator) (rats = STAR) (BINARY STAR) Castor (BINARY STAR),
7 Broadcasting (ON THE AIR) is another (another) problem (= anagram indicator) (another = ON THE A-R) around Ireland (-I-) (ON THE AIR),
13 Party (DO-) with very small (-MINI-) drinking vessels (-CANS) (DOMINICANS) in The Abbey (DOMINICANS),
14 It’s all the rage (hot = HO- -T) over detective (private investigator = -P I-) (HOP IT) getting on your bike (on your bike! = HOP IT),
16 Oriental (East = E-) provides wrong (-X-) answer (-A-) in moral (moral = ORAL -M) exercise (= anagram) (ORAL EXAM) putting Chinese to the test (ORAL EXAM),
17 Most of those in 1 down (most of ‘Romans’ = ROMAN-) from church (Church of England = -CE-), school (-S) (ROMANCES) and courts (ROMANCES),
19 Fresh (= anagram indicator) tapas (tapas = PASTA-) and endless (end ‘lesS’ = -S) (PASTAS) types of European cuisine (PASTAS),
21 Code (code/key = LEGEND), for example (e.g. = -EG-) discovered in advance (L-END) (LEGEND),
23 Intense tee off (‘intense’ ‘tee’ off/ without ‘tee’ = inns = INNS) by a number of the locals (INNS),
24 State (= homophone indicator) travel (‘roam’ = ‘ROME’) and capital for those in 9 across (ROME is for the capital for ‘Italians’).