What if your partner's father gifts the site into your joint names - would this make any difference re amount of tax payable?
I think they had their solicitor draw up an agreement, which will be void once they marry. It gives the value of the site to him but the value of the house is joint, if they ever go their separate ways and the house is to be sold...
wishful thinking, I'm afraid. In common with other, more famous, 'pre-nups', they are not recognised here, and once married, the property of both will become property in common.