Gifting half the house tax liability

[Zippyworld]

My missus wants to give me half ownership of our house. We are not married.
We have lived together for 15 years and have two dependant kids.
There is £100k left on the mortgage. Its value is £650k.
The mortgage is in her name.

The question is will either of us be liable to pay any tax if we do this ?

I realise that we will speak with a solicitor and the mortgage lender, but first shout is the taxation rules.

Advice would be greatly appreciated

[Zippyworld]

I have had more helpful answers, thanks anyway.