Selling house, repaying morgage?

I have a mortgage that has an early repayment claus. If I pay off my mortgage before may 1st 2011 I have to pay the bank �2500 in early repayment fees. I am selling my house and have an offer. If I accept the offer and set a completion date for a date after may 1st. Would I have to pay the �2500? In other words at what point during the house selling process does my mortgage get paid or can I pick the date that this happens?