Not across.

Down clues are normal, across clues are not.

Across:
8. Fish residents of the operating theatre (8)
9. Penned in, but achieved assistance (6)
10. Brief Celtic language (4)
11. Able to be affirmed, as expected (10)
12. By this or by that (6)
14. Lead the musicians he was responsible for (8)
15. Talked nonsense and with a silly walk (7)
17. Lived forever in sin (7)
20. Find out if unmarried, in the old-fashioned way (8)
22. Hid, covered by ribbon (6)
23. Large of body and large of mouth (10)
24. Roosevelt was contrary to the main direction (4)
25. Working, working in the engine room, perhaps (6)
26. Journeyman who ties one up in knots (8)

Down:
1. Through and through takes turn with a woman in childbirth (8)
2. Monster gore-fest (4)
3. Roman general's favourite football team? (6)
4. Senesce ungracefully: that's the central message (7)
5. With cognovit, legally he confessed and came into grief (8)
6. French city, cute, hides computer resembling a sausage (10)
7. In good health, that is slang for aggression (6)
13. Aid near, if poorly, with medic within heart membranes (10)
16. Imagine, in French, a facial expression (8)
18. It's here they toss the caber, (Dee nearby) (8)
19. Neat! A railway first (7)
21. With a slant in any recital I choose (6)
22. No food, feature of Venezuela (6)
24. Slippery fishes have the measure in points (4)