Can I delay settling mortgage to avoid ERC??

I want to put my home on the market but my fixed rate mortgage deal doesn't expire until 30th September. I'm not making an onward purchase, so my question is: if I sell my property before then and am likely to complete before end of September, is there anything to stop me delaying settling my mortgage by several weeks, in order to avoid paying a hefty ERC?

I'm guessing the flaw to my cunning plan is that the mortgage lender will not release the deeds until the account is fully settled?

Can anyone who knows about these things please tell me whether there is a loophole here or not? Thanks!