Until recently HMRC have been very supportive of IVA's, however, recently they have taken the line of recovering unpaid tax by other means, where the prospect looks inviting.
If they are the majority creditor (over 75% by value) they can refuse the IVA, if they are not and the IVA gets accepted they are still bound by it.
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014
Have a chat with a couple of companies - Andy Davie/Vincent Bond (details under the expert link on the left hand side of the page) will give you some free advice.
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