Common sense has prevailed, after giving my completed IVA company the option of letting me take the cash sum, or I'd take the sum off my mortgage so there was no money for them to get there hands on. They have admitted defeated in there pursuit of the sum and a nice fat cheque came in the post this money.
Think it's time to print a few more of these template letters from MSE website!
Your IP should probably have pursued any potential PPI claims whilst the IVA was up and running. Only you can now determine whether claiming money back from creditors who agreed to write off debts through the IVA, or were assets which existed at the time of your IVA, feels right - but I don't think that anyone would knock you for doing this especially as you have held consultations with the former IP.