I would certainly agree that you need to clarify this with your IP just to make sure how things stand.
Sharing from experiences of dealing with debt
The greatness of a man is not in how much wealth he acquires, but in his integrity and his ability to affect those around him positively.
Bob Marley. http://kallis3.blogs.iva.co.uk
There is nothing difficult about presenting an IVA case if Northern Rock are a major creditor. We all know what criteria they work to, and you will be informed by the IP of your choice as to whether your case is likely to be acceptable.
Personally I find Northern Rock one of the most commercial and easiest creditors to work with.