No, if you haven't applied for a particular box,it's two at least,possibly three.That said, as the poster above says if you are somewhere like London you could go straight into a seven etc.
It's a great job,but make no mistake you will have to know your stuff,both during and after Signalling school.When you are being interviewed,safety and communications are paramount,and when you do start properly, every word you speak over the phone is recorded.You have lead responsibilty over everyone bar an ECO,so if say a Driver doesn't repeat your instructions back and you don't remind him,it's you that gets the bollocking, not him,and the same goes for COSS's PICOP's , MOM's,and everyone else you deal with.
Anyhow one step at a time,get the job first, and remember what I said about safety and communications.....