Purely 'thinking out loud' as the answer is rarely black and white ........ The redundancy pay you are allowed to keep is to cover your living expenses and the IVA payment while you seek work. Any benefits you get while doing this would be deemed as extra income and will increase the monthly IVA payment accordingly. In theory if you get to keep 6 months redundancy and find alternative employment within that time, say, 3 months in, you should give back the 'unused' portion (3 months in this example) of redundancy compensation.
Your IP could, possibly, take the benefits income and allow you to retain the difference between that figure and your old salary and then give the rest back.
There is a lot of interpretation and discretion built into IVA's, so you would really need to see how your own IP would act in the circumstances.
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014 http://foggy.blogs.iva.co.uk