Cryptic crossword No 931

Across

1. Sailor captures a flag, mangled after resistance, in battle (9)
2. See 5d
3. How often should 'u' appear in this grid? Site forum's confused (4,5)
4. Look around tower (4)
5. See 15d
6. Secretary to politician starts to have lewd thoughts about electronic publication (8)
7. See 10
8. Posh Londoner with mortgage in home counties (6)
9. They might be rotating in a 4-4-2 formation (6,6)
10. Hybrid fish caught with sight condition (5-4)
11. Shape in 9's element of crossword, unusually (8)
12. Test model railway (3)
13. Overheard description of Dr Beeching's chopper on farm (4,6)
14. See 4d
15. See 22
16. See 30d

Down

1. Recent changes following naked party for creative venue (3,6)
2. Haircut with short back and sides for Romeo (4)
3. Pall cast over ancient city 'Olympics'? (6)
4. Going to work on name... Clare, perhaps? (6,4)
5. Part of a foot (or of bone in chest) (3,4)
6. See 20a
7. See 1
8. See 21
9. Part of grand plan originally sees Scot meeting Russian (5,3)
10. Fairy-tale flyer, something Jack steals from giant, not as warm with heat oddly lacking (5,6)
11. On the radio, solver listened to rock station (6)
12. Ben and Niall playing a sort of pool (4-4)
13. See 17
14. See 26a
15. Attract notice finally with case of nicest diamonds (6)
16. Group of women with quiet desire (4)
17. Established group (3)
18. After wine, I select crackers, with hesitation, for cheese (3,9)