Adding name to property/title deeds in order to remortgage

Hello everyone,

I am currently researching the feasibility of building a self contained basement flat below my mother's property. We are the freehold owners of a mortgage free maisonette and reside on the ground floor whilst our neighbours live on the first floor. Our property has recently been valued between £775k to £800k.

Recently I have obtained quotes from several building specialists and estimate the excavation, underpinning and fit out cost will be no more than £325-340k. The idea is to use savings and remortgage the property to bankroll the project. I need advice on whether this would be possible by adding my name to the title deeds in order to remortgage at a lower rate?

If the above is possible, I am concerned the bank will decline on the basis I am seeking to build a new flat. The other concern is whether this would result in unforeseen stamp or inheritance tax.

There are a number of other factors to consider although an early steer on the above would be welcomed before going into further detail.

Thanks in advance for any replies! !!!65279;