UK Tax Questions? Ask a UK Tax Advisor for answers ASAP
If your mother makes a gift to you of the cash she received for the property, then that will be a potentially exempt transfer which will remain as part of her estate for Inheritance Tax purposes for seven years after it is made. Howver, the potential IHT charge starts to taper away after three years as you will see here. You should remember that your mother may have CGT to pay as a result of the sale of the property to you so she may need some of the cash you paid via your mortgage for it to settle that liability.
As far as you are concerned, you should check with your lender whether there are any early moergage redemption penalties that you may have to pay.
I hope this helps but let me know if you have any further questions.