Are you sure you are in an IVA ?
If you go to this website ...
http://www.insolvency.gov.uk/eiir/ and enter your name details it will tell you.
I am not sure CCCS can provide IVA's, though they can recommend you to an Insolvency Practitioner.
If you are in an IVA, then NatWest can add interest and charges only up to the time your IVA was approved.
Your Supervisor will be aware of this - again their details, if you do not know them, will be on the link above. They wil only allow NatWest to prove their debt with interest and charges up to the date your arrangement was approved - January 2005.
You may wish to ask your Supervisor to confirm to NatWest that they are bound by your arrangement and its terms.
Tell it like it is.
Tell it like it is.