to re-mortgage or not to re-mortgage?

Beck__3

I have a little dilemna and would appreciate any advice you guys can give.

My current situation is as follows...

I have an interest only flexible mortgage with Coventry (2.5 years into a 24 year term), current rate = 5.55%, outstanding amount = £100000, exit fee = max £190. I can make overpayments/lump sums when I like. I am currently overpaying every month to the amount of a normal re-payment mortgage (Im paying around £650 total per month). My house is worth around £120000.

I have around £35000 in savings, £13000 in an ISA, rest in an ING account.

My current thoughts are to use some savings to pay a lump sum off my mortgage. So I have decided to pay off £20000 which will leave my ISA savings intact. My outstanding amount will be £80000.

I predict that the rates may go up again soon so Im considering re-mortgaging to a 2 year fixed deal. After that I could be in a position to buy a new house or just re-mortgage again.

I work for HSBC bank and one of the perks is that they would pay me a subsidy towards my mortgage if I had an HSBC mortgage. This works out at around 1% discount each month. I can re-mortgage to HSBC for free (no fees) at a 2 year fixed rate of around 6%. With my discount this will work out at 5%. I of course would have to pay an exit fee to Coventry of around £190. This would be a re-payment mortgage which is fine as I want to pay off the capital asap. However I could only overpay by 20% each month which does take some control from me albeit only for 2 years.

I was thinking if I did re-mortgage that I would get a 15 year term for £80000, which would work out at around £660 a month (on 6%), I would then most likely overpay the 20% each month using my discount etc.

So any advice would be appreciated. Any issues with my plans? Is there an obvious better way to do it? Thanks in advance.