To be on the safe side I would let them know, they may allow you to keep it all.
Better to be honest.
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
As Kallis says always advisable to drop them a line or telephone through to advise them and they'll advise accordingly, however with ever increasing prices it may be as Kallis says and their advice may be to use it and review again at your annual review.
IVA final payment left the bank on the 26th January 2013...looking forward to a debt free future.
I had a pay rise last year of £47 a month which was just before my review, so i made my IP aware. my monthly payments were not increased as with inflation (even though they keep telling its lower but my food bill keeps rising) it was quickly gone. So its best to let them know.