You need to speak to your IP and explain what you have done. They may give you time to pay it back.
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
It is best to confess now than be discovered later. They are more likely to assist, possibly by adding the amount to your monthly payments as arrears --- they might add the number of payments needed to cover this amount (50% of the bonus .... maybe a bit less if you have the 10% disregard in as well) on at the end of the agreed term. Some IP's however would prefer the arrears dealt with in the 12 month period, so you might be able to make increased payments for a short while.
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