porting mortgage to lower value property

peppapig14

we are 2.5 years in a 5 year fix with Nationwide
we want to sell our house ( going on market in next few weeks ) and purchase a  flat 
due to equity in our house we would only require our mortgage on the flat to be half the value of what we have left on our current mortgage
how does porting to lower property work?
 would we still have the same amount of mortgage as we currently have on our house or would we use our equity to pay some off and only half a mortgage for half the amount ?

kingstreet

You port the amount you need for your next purchase and pay any ERCs on the amount left which has been redeemed from the sale proceeds. The remainder of the sales proceeds is your "deposit" for the new purchase.

EG

£400,000 sale less
£300,000 mortgage
________
£100,000 equity for deposit.

then;-

£300,000 purchase
£100,000 deposit
________
£200,000 new mortgage (ported rate) leaves

£100,000 redeemed attracting ERC.