My daughter,s just moved in with her partner it is his house

Hi, thanks for your question. I am a qualified family law solicitor.
He can change the will whenever he wants as it is his choice what he leaves in a will.
Your daughter will have no automatic right to any inheritance if he passes away, and if there is no will in place his estate will go to his children. Your daughter will have a right to make an application for a share of the estate, however this will be fought out with his children and can be lengthy and costly.
She should also be made aware that the contributions she is making towards his mortgage will not automatically give rise to a share of the property. As they are unmarried his property is his. She should therefore consider discussing a cohabitation agreement to secure the contributions she is making.
If she were to marry him, then the rules will be different and she will have an automatic right to some of his estate if there is no will.
Please let me know if you have any further questions regarding this.