Could you provde some further info as to why you want to go bankrupt, given that you are currently in an IVA? How far in are you?
You first need to check the terms of your proposal(as modified)to determine the circumstances under which the Supervisor can present a bankruptcy petition and any provisions for retaining funds to do so.
If you are struggling with your IVA, the first port of call is your IP as it may be possible to do something for you as a short term measure at a difficult time.
If you are petitioning because you have received correspondence from a third party that says you are better off going bankrupt than you are in an IVA, you need to think extremely carefully about what you are doing. Just have a quick read of this topic ...
http://www.iva.co.uk/forum/topic.asp?TOPIC_ID=11571
Tell it like it is.