You do automatically go to your firm choice if you get your grades. You will need to ring Swansea up and asked to be released into Clearing, but speak with RHUL to ensure you have a place if you were to do this first. Try and start this process as soon as possible on results day, as phone lines will be busy. This is partly why I suggest contacting Royal Holloway now as you can establish contact because knowing who you are will speed up the process (hopefully, no guarantees but every little helps so they say).