Ask your current mortgage provider for redemption figures. This is what it will cost you to discharge the mortgage entirely and recover your title deeds.
As it seems to take forever for banks to seal a paid off mortgage, you are probably better off asking your solicitor to firstly take up the Deeds from your lender and then redeem the mortgage.
If you are discharging the mortgage from the sale proceeds, your solicitor will not be able to part with the deeds until s/he has sufficient funds to discharge the outstanding mortgage.
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