I rather think you will have to pay it into your IVA.
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
A lot will depend on the reasons for the rebate (self employed, CIS, etc.) and your current status, as well as the opinion of your IP and only your own IP can say, for certain, which way he / she is going to jump.
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