I recently started working in the Uk and I applied for a NI number through my employer. This was over 6 weeks ago.
I was told that since I have applied through my employer I wouldn't be called for an interview. After weeks of waiting, I finally got a letter from jobcentre plus. I assumed that it would have my NI number on it, but it is an invitation letter for an interview. 
Is this a bad thing? Do I need to worry? If they call you for an interview, does that mean that there is an issue with the application? I have no idea how this whole process works, but I'm quite overwhelmed by it. :(
I sort of assumed that getting an NI number was a given, but the letter states that they will "decide whether to give me a NI number". This terrifies me and I've now imagined all sorts of scenarios in my head where I am refused the NI number.
Could someone explain the reasons why somebody's NI number application would be refused?
I have no criminal record and I have permission to live and work in the UK. Do they check for other things as well? Is it like a check for defaults (credit check)?
I know I'm getting very worked up about this but this job means so much to me and I don't want anything to jeopardise it.