I39;m looking to switch our mortgage from Repayment to Interest Only

I have split up with my partner and we would like to rent our flat out until the property market recovers. We are with Nationwide and it seems we can switch to Interest Only but as part of the condition of this we must have an ISA/endowment policy in place alongside this. We are really doing this to reduce the cost so does anyone know how much banks would insist on us paying into an ISA? The current repayment monthly amount is £1407 and taking it to Interest only brings it to £930Thanks
      Answer1:Interest only loans is what started this mortgage mess. People were never able to build up equity in our homes (anyone remember the name Quicken Loans - yup - they started this fiasco.)Then came the ARMS and options and all hell broke lose.Whatever your choice, please realize that interest only is not really saving you any money. Its just making banks rich./
      Answer2:There is no minimum amount you can pay in each month but on my ISA im only allowed to put a maximum of £3000 pound in a year. The interest on them isnt that good at the moment either with the financial climate and such, but good luck to you, i have a mortgage with nationwide but was told id have no chance switching to interest only because of the rates going down. If i were you id look around different banks to see what ISAs they have to offer mines with halifax, the interest rate is good but theres that limit on how much you pay in but im sure they can extend it. Just shop around till you find the best one :D