Cryptic crossword No 3,728

Across

1. Father given hundred inside pay packet for holy work (6)
2. Island-hopping regularly for an hour (4)
3. Girl smuggling ring in prison (4)
4. Swamp is leaf university, perhaps (5)
5. Rioting from promotion within gun department? (2,2,4)
6. I smashed units where they stood (2,4)
7. Flower : initially, tulip yields no extracts (4)
8. Idiot - hold a second - hit me! (5)
9. Chooses surgery time and speed (4)
10. Rodent with inner quiet is attentive (4)
11. Arrival could be unstable (6)
12. Mad European vermouth succeeded (4,2)
13. Loner taking in untruth, becoming even more isolated (8)
14. Credit to computer department in charge of Alabama - it's essential (8)
15. Alice's mad friend on board is destroyed (8)
16. Hotel's neighbour to hunt for outdoor space (4,6)
17. Alien shackled in iron for event (4)
18. Three in one for Italian (10)

Down

1. Root, we're told, is weight (5)
2. Beer spilled on shirt and hat (5)
3. I result, bizarrely, in one who's more eager (7)
4. Noble sad for preparation (9)
5. Sellsword's payment having right to pierce (9)
6. Bass lay rearranged from the depths (7)
7. Bury machinery (5)
8. Of note: student's after meat (5)
9. Energy lotion containing copper giving power of speech (9)
10. Manage New York without bearing sign of cold (5,4)
11. Holiday over the east end of Prague was rubbish (5)
12. Green rain falling on Rhode Island, giving mixture (3-6)
13. What children do where boards are trod? (9)
14. Main character? (5)