Gifting money to son for a house that I will be sharing with him

I am looking at helping my son buy a bigger house so I can live with him and his family. I have been told that if I live for more than 7 years then the gift is tax free. However I have also been told that if I live with him rent free then it is not a gift but a benefit in kind so it does not qualify as a gift..is this true?

Hi,
If you give something away but still benefit from it (a ‘gift with reservation’), it will count towards the value of your estate.  
There is more information on this at:
Work out Inheritance Tax due on gifts
Thank you.