How much can I remortgage for?

InMyDreams

I'm on a rough deal for another year and three quarters (5.3% fixed) but I've done the sums redemption penalites don't make it worth moving. At the time we accepted whatever our current lender would give us as we weren't in a position to shop around. And even then we were lucky enough to be able to shift even more to interest only.

Circumstances have now improved (as expected) and we are in a position to start overpaying. (Or at least matching what we would be paying if it were a repayment mortgage, and some...) I am also confident that come Jan 2008 we will still be in a strong position to shop around.

So here's my question...

When we do come to take out a new mortgage, is the amount outstanding on our current mortgage relevent to what we remortgage for? In other words, any extra money I pay in now, I can get my hands on again if necessary when we remortgage, right? The new mortgage would simply pay off the old and give us back our savings? There are no extra complications/charges in that? I obviously don't want to feed *all* our savings into it, leaving us with no cushion, but I might be happier topping it up some more if I could treat it simply as a 21 month saving plan that I can't withdraw from? Or is there something I'm missing? Obviousy I'd hope I could leave it all there, but it's always nice to know there's an option.

The only negative I can see is that if circumstances take a turn for the worse again, and we don't have the income to justify the mortgage again and find ourselves stuck again, our savings will be tied up again on the next 'deal' and won't be available to cover our payments for any 'lean' months.

I'm just trying to get my head around how much of our saving to risk into the mortgage, given that on our current allows us to over, but not under-pay.

TIA,
IMD.