18.

14. Joan Jett

20.
19.

1.  All together (boyband started in the late 90s)

2.  Following The Queen - THE KORGIS
3.  When Halloween is over - ALL SAINTS
4.  The beat in Alaska - SNOW PATROL

5.  Can't Wait (mid 2000s group)
6.  Waiting with a ring (US singer)

7.  Corporate kissing - LIPPS, INC

8.  Insane inmate (one word answer)
9.  Damp in defeat (one word answer)
10. Rider in London SE9
11. Chief Mint
12. Mixed-up accusation (current singer)
13. When Livingstone met Stanley
14. Keeping up with ease (singer started out early 80s)
15. Beware of the dog
16. Early riser in Philadelphia
17. Wet weather in Lancashire - FLEETWOOD MAC
18. A female living in Maryland? (mid 80s one-hit wonder)
19. Almost an emergency (early 70s band)
20. An unusual assembly

20. good but not my answer
14.

1. NSYNC Cauthen

you should be having a go on No 10, Cauthen

8. very close but not the answer I have

I'll give some hints and maybe some rewording next list

Afternoon squares/guys
14 Kylie Minogue

1.  All together - NSYNC
2.  Following The Queen - THE KORGIS
3.  When Halloween is over - ALL SAINTS
4.  The beat in Alaska - SNOW PATROL

5.  Can't Wait (mid 2000s group)
6.  Waiting with a ring (US male singer)

7.  Corporate kissing - LIPPS, INC

8.  Insane inmate (one word answer, one-hit wonder Scandinavian duo)
9.  Damp in defeat (one word answer, group from the late 70s)
10. Rider in London SE9 (perhaps I should have said Jockey)
11. Chief Mint (one-hit wonder singer/actor)
12. Mixed-up accusation (current singer)
13. When Livingstone met Stanley (late 70s goup)
14. Keeping up with ease (singer started out early 80s)
15. Beware of the dog (group, one-hit wonder from the mid 80s)
16. Early riser in Philadelphia (female singer)
17. Wet weather in Lancashire - FLEETWOOD MAC
18. A female living in Maryland? (mid 80s one-hit wonder)
19. Almost an emergency (early 70s band)
20. An unusual assembly

15.  good guess but not right

10.

18 tori amos

1.  All together - NSYNC
2.  Following The Queen - THE KORGIS
3.  When Halloween is over - ALL SAINTS
4.  The beat in Alaska - SNOW PATROL

5.  Can't Wait (mid 2000s group, if you can't wait what are you?)
6.  Waiting with a ring (US male singer, think along the lines of a proposal)

7.  Corporate kissing - LIPPS, INC

8.  Insane inmate (one word answer, one-hit wonder Scandinavian duo, Mad???)
9.  Damp in defeat (one word answer, group from the late 70s)
10. Rider in London SE9 (perhaps I should have said Jockey, think of a South London football team)
11. Chief Mint (one-hit wonder singer/actor, think of types of mint)
12. Mixed-up accusation (current singer, think of another word for accusation)
13. When Livingstone met Stanley (late 70s group)
14. Keeping up with ease (female singer started out early 80s, my extra clues make it too obvious)
15. Beware of the dog (group, one-hit wonder from the mid 80s, why would you be wary of a dog?)
16. Early riser in Philadelphia (female singer, where is Philadelphia?)

17. Wet weather in Lancashire - FLEETWOOD MAC

18. A female living in Maryland? (mid 80s one-hit wonder, sort of novelty cheesy Europop)
19. Almost an emergency (early 70s band, think of another word for something being an emergency)
20. An unusual assembly

6.  NEIL DIAMOND before the extra clue, WD Aspro

18. it's not a female singer

15. IT BITES WD PP before the extra clue

8. MADCON nec, really UL Aspro, Madcon probably too recent for you!

1.  All together - NSYNC
2.  Following The Queen - THE KORGIS
3.  When Halloween is over - ALL SAINTS
4.  The beat in Alaska - SNOW PATROL

5.  Can't Wait (mid 2000s group, if you can't wait what are you?)

6.  Waiting with a ring - NEIL DIAMOND
7.  Corporate kissing - LIPPS, INC
8.  Insane inmate - MADCON

9.  Damp in defeat (one word answer, group from the late 70s)
10. Rider in London SE9 (perhaps I should have said Jockey, think of a South London football team)
11. Chief Mint (one-hit wonder singer/actor, think of types of mint)
12. Mixed-up accusation (current singer, think of another word for accusation)
13. When Livingstone met Stanley (late 70s group)
14. Keeping up with ease (female singer started out early 80s, my extra clues make it too obvious)

15. Beware of the dog - IT BITES

16. Early riser in Philadelphia (female singer, where is Philadelphia?)

17. Wet weather in Lancashire - FLEETWOOD MAC

18. A female living in Maryland? (mid 80s one-hit wonder, sort of novelty cheesy Europop, not a female singer)
19. Almost an emergency (early 70s band, think of another word for something being an emergency)
20. An unusual assembly

5 - Impatient? (Will Guess)

crystal gayle 10

10.

5. KEANE pp

13. but getting closer