Cryptic crossword

ACROSS

1. Shellfish to pop right inside (5)

4. Punished for having passed last runner after a second (7) 8. Following mathematics in the US, a second mowing (9) 9. Small flatfish gives one a rotten return (3)

10. Last three children backed by you French make one jumpy (7) 12. Bathroom powder: vital cleansing ingredient (4) 14. Musical note a lazy leader will render in the smallest way (7) 17. Heights as achieved when retaining the record (4)

18. The agony of being wrong at law and certain not to begin (7) 20. At home to Kelvin, writer commits it to paper (3)

21. With justifiable anger dining out with non-u Aunt (9) 23. What Götterdämmerung brought about was a gift from heaven (7)

24. Stratum of early formation (5)

DOWN

1. No mincing words, pal: pine, asking for it! (5,8)

2. One’s dress one might treat differently (6)

3. Such a drug might be turned into crack endlessly (8) 4. The main time of the year has been halved (3)

5. An insomniac heaves at the pain he has to bear (4) 6. Man with pack, misled in Paris, is quitting (6)

7. Cold letter Cob got from one out dunning for payment (4,9) 11. Some time at work: move it! (5)

13. Song in parts it’s crazy for a girl to get wrong (8) 15. Editor rejected drink with drug in it (6)

16. After fifty, can you have nothing to lose? It’s madness! (6) 19. It’s a long sentence for a biographer to produce (4) 22. Bad cheque may be given over as well (3)