1: Cheaper oil, gas distributed in Island chains (13)
2: Apprentice relinquishes heart to temptress (7)
3: Servile son, first prodigal (7)
4: Central matter for physicists luncheon: rocks releasing hydrogen (7)
5: Places for vacations, quiet intervals or breaks (7)
6: Hot burnt residue is on hot pot (7)
7: Rear oat variety as a way to break up the soil (7)
10: Canadian water ordered for regal tea-break (5,4,4)
16: Dexterity is an insult, so we hear (7)
17: Machine spindle starting to mistime; also about to begin labouring (7)
18: Endless barbecue arranged for young carnivore (4,3)
19: Importance of history (7)
20: Dog leaps in, frolicking (7)
21: Coral Sea, perhaps, without a fish (7)