Whether you are granted or not depends on many factors such as
- Reason for seeking asylum (political, religious, etc)
- Country of origin from which you are seeking asylum
- How you got all the way here in the UK
- Evidence you have to backup your asylum case etc
I'm not sure you get detained immediately but your case will be considered. I suggest you get yourself a good lawyer who will look at the details of your case and advise you on how to go forward. You may wanna approach the Citizens Advice Bureau for help and they can also direct you.
You might wanna look at the Country Policy in the preparation of your asylum case to see what policies,understanding the UK Government has on your country of origin.
https://www.gov.uk/government/collectio ... tion-notes