Caporegime
This might sound harsh so bear with me here.. What's the worst that can really happen? If your mortgage gets to a point that you can't afford it then let it go if it came to that point.. The property if never really yours until it's paid off anyway.. You'll have a bad debt for a few years but heck.. You can rent and you've lost nothing. I know loads of people who have done this.
On the contrary, any overpayment's on a flexible plan will trim back the principle loan which in turn will reduce your interest repayments over time... You might as as well do this whilst rates are exceptionally low. You'll save a fortune of interest and the mortgage will mature early. As I said earlier, most flexible mortgages allow a "nest egg" which performs the offsets and if you need to delve into it to cover part repayments, then it's there but the you've taken full advantage in the meantime.
If you've fixed your mortgage say at 4% for 5 years, and the rates don't exceed this until year 4, what have you really saved? Possibly one year.
1) Most fixed rate mortgages allow you to overpay anyway. I can overpay up to 10% of the outstanding capital per year without incurring early repayment charges.
2) It still comes down to how you value possible savings against peace of mind. Some of us would rather have peace of mind and guaranteed outgoings.

