1: Visitor made an estimate when audited (5)
2: Law, say, constraining trade union leaders (7)
4: Come before chief of police, and back off (7)
5: Trains without commanding officer and suffers (5)
6: Mongrels at each others' throats in this ruthless world. (3, 3, 3)
7: To fight sunburn, he faced pain unflinchingly. (7)
8: At first, Sonny and Cher having bizarre duel with one providing slots? (9)
13: With greater reason for a riot I riot (1,8)
14: Columbine takes stage during repeated Iolanthe opening, in blue-green (9)
17: Saturday: Wild nature walk (7)
18: Surrounded, small insect crawled into cover (7)
19: Am I nuts fighting this terrible flood? (7)
21: Material extracted, sent back (5)
23: Actress Dern's starting to like distinctive atmosphere (5)
24: Does loose change forfeit worn tail for false head? (5)