Inspired by jafe's Cryptic with missing capitals and Tzu Li's Tokyo Metro puzzle:
Solve the clues and fill the grid. Each clue is missing a different London Underground Station
As jafe has noted in Traversing Africa: A Cryptic Journey:
By request of the Sanity Preservation Institute, some long names have been shortened. For example, if the full place name is "Xyz Royal National Park", the answer will be just "Xyz" (often with "royal national park" or similar as the definition).
Now, here we go: ** Edited clue for 12D to enhance clarity
Text transcription of clues:
Across:
1. Big at first, ?? without direction is flash of lightning (4)
2. Limits of ?? shows time of year (5)
3. Initially courteous, ?? is king out of lair (7)
4. First half of ?? watched Polish city (6)
5. First slice of ?? blended becomes little boy (3)
6. Beheaded ?? misheard as nation (7)
7. Head-on horse on ?? With alien makes protective accessory (6)
8. ?? without misheard alarm matters dimensions (4)
9. A situation around the head of ?? being Anglican (12)
10. Bizzare ??, with two more piece of instrument (8)
11. Talk rudely below the ?? (5)
Down:
1. Dark part of messy ?? is unprecedented event (5 4)
12. Nameless ?? in the past: evil (6)
13. Shortened church ahead of ?? without meat is meat (7)
14. Poor ?? with leg crossed wounds (5)
15. Extreme ?? in shallow hot open pool is diagonal wanderer (6)
16. Scrambled ?? following the Honourable with initialized Delhi University is American country (8)
17. Counting section in ?? renders fortune symbol (5)
18. Safari ?? conceals master in enigmas (5)
The grid:
Failed in an attempt to achieve symmetry :(