Tell your IP he needs to take specific legal advice on this point. There have been a couple of test cases lately on this very subject, and my professional opinion is that this charging order cannot be properly registered due to the existence of the IVA and the fact that the creditors is probably legally bound in.
If the IP does not understand this, I am happy to chat to him off line and suggest an insolvency lawyer who could help. I have some concerns that you did disclose this debt, but that it was incorrectly detailed within your proposal as if the charge had already been created.
Mortgage Express are a fairly well known sub-prime lender, and Drydens are good commercial lawyers who will fight their own client's corner to the best of their ability - as all good lawyers will do. I confirm my suggestion that your IP seeks his own legal advice with regard to this issue, given the size of the debt concerned.
Regards, Melanie Giles, Insolvency Practitioner for over 20 years.
View my IVA blog at:
http://melaniegiles.blogs.iva.co.uk