Why is the UK not in Schengen?

Related questions

1. Why is Ireland not a Schengen country?
2. How long does Ireland visa application take?
3. Can I visit UK with Ireland Visa?
4. Can I go to Ireland with UK visa?
5. Why is Ireland not Schengen?
6. Why is it called Schengen?
7. Why is Ireland not in Schengen?
8. How can I apply for PR in Ireland?
9. Who needs visa for Ireland?
10. Which country has free visa?

Tags

1. #anyone
2. #borders
3. #opted
4. #criminal
5. #namely
6. #citizens
7. #policing
8. #however
9. #still
10. #controversial
11. #parts
12. #controlled
13. #other
14. #system
15. #entry
16. #schengen
17. #words
18. #regards
19. #rules
20. #controls