If I were the enter an IVA and then decide I want to go back to how things were, meeting my payments as was (can't think why I would, but I really want to know where I stand in every eventuality here), would that be possible?
What would normally happen is that you would miss 3 payments and have your IVA failed. That way you could go back to making normal payments. You would probably find though that any money you have paid in (depending on how long you had been in one for ) would just go to pay your IP's expenses.
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.
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In theory, if your IVA were to fail, there is nothing stopping you dealing with your creditors on contractual terms again, but I cannot see how this would be possible unless you had a major change of circumstances.
Most of your debts will actually be sold on after the IVA has been accepted, so it will not be the same companies that you will deal with in the future.