It is usually all paid across to your IVA unless it reaches 100% of your debt plus fees.
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
Throughout the PPI saga, different IPs have taken different views and actions and, often, the same IP will have changed those views and actions during the course of time (just to make life easier for us !!).
Somes firms have, in the past, allowed you to keep the first £500 of claims, others have allowed you to keep the interest element but most take it all.
The firm who acted for me, tool all of my refund, including interest and, a couple of weeks later, decided to allow interest to be kept --- but wouldn't give mine back to me. Currently they are, once more, dangling the "keep the interest carrot" ( I would say "don't hold your breath"!).
So -- the simple answer is that it depends on the weather and what your IP had for breakfast that morning!!!
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014