We owe £42K in unsecured debts and we have a mortgage of £145K. After becoming increasingly impossible to keep up with minimum payments on visa cards and loans we decided to apply for an IVA with ClearDebt but unfortunately it has been declined

the reason being our mortgage goes from being a fixed to variable rate with the Northern Roack in June and that will put our current expenditure up by £300 per month (Interest only payments at that!) so that blows our expenditure over the minimum payment for an IVA to be accepted.
Also, the MBNA are now threatening to put a charge on our property of £10K so we wouldnt get alot if we sold our property minus solicitors, estate agents, surveyors etc.,
Ive read on this forum that if we got a private rented property and gave up our house then went bankcrupt the house and the unsecured debts would both fall into the bankcruptcy charge and we wouldnt be liable for any shortfall should they sell the house at a shortfall?
Im at my wits end and dont know what to do for the best? Please help!