Abbey Flexible Plus Mortgage Questions

Couldn't say. It would be interesting to discover on what basis they calculate this "term". Are there regular funds flowing into the non savings pot part of it? Are they of the order £82.8k divided by 11.75 years, i.e. around £587 per month?

It could well mean that they consider the £37k as "paid off" the £100k, leaving you to clear a further £63k balance over the course of the next

So yes, in that case, I think it probably means that over 11.75 years the level of your regular payments would reduce your interest-costing debt from £63k to zero, or put another way, your total debt of £100k would have reduced to the value of your savings pot. At that time you could then decide whether to use the savings to pay off the remaining debt, or to continue making payments, but you wouldn't be charged any more interest, though you would presumably start to earn savings interest on that part of your savings pot which exceeds your remaining loan debt.

Yes, the monthly payments are currently 584 per month.

I have the same mortgage: Abbey changed it to interest only without telling me. Monthly payments are fixed based on the interest for the total loan amount and take no account of the offset amount. It gets complicated because the monthly payments are no longer the true interest so some excess goes into capital repayments which are different to the offset pot.

Previously with the same mortgage I achieved the happy state of affairs of zero balance. This of course meant no more monthly payments. It could be at the end of the term you need to redeem/re-mortgage (so more fees to pay..). But I recall the newer versions of this product are marketed as 'lifetime mortgage'.