joanne
If your IP does not agree to put what appears to be a very reasonable variation to address your arrears, and continues to petition for your bankruptcy, you can attend Court and object to the application.
I think you would very likely succeed, but do be absolutely sure that you can afford the new level of payments you are offering. Make sure you have left adequate provision for contingencies, such as house maintenance, medical expenses, car maintenance and clothing.
You must speak to your Insolvency Practitioner direct and ask him/her why they will not allow you to do this. Please don't worry, you are doing the right thing by trying to resurrect the IVA, and should feel proud that you are continuing with your obligations towards your creditors.
Regards, Melanie Giles, Insolvency Practitioner for over 20 years.
View my IVA blog at:
http://melaniegiles.blogs.iva.co.uk