Thanks for your question. I will try to help.
First of all, if you and you partner presently hold the house jointly (as joint tenants) then each person's share would pass to the other upon death regardless of any directon made in any Will. If this is not what you want then you should sever the joint tenancy by using Form SEV from the Land Registry (you will have to send it to them and if you have any questions about completing the form you should call their customer service number - they are very helpful):-
You will then hold you interests as tenants in common, meaning that your respective shares will pass according to their wills or under the intestacy rules. Your partner need not sign the form provided you follow the instructions.
Basically, you will receive whatever you actually negotiate and agree.
Unless there is a declaration of trust (for which you must hold your property as tenants in common) then there is a presumption that each party retains a 50% interest in the equity in the property .A declaration of trust (had you executed one) would state that you hold your interests in the properties in specified percentage shares and it could also say that each person only retains their 50% interest in the property subject to equal contributions to the relevant outgoings for the property. If your partner had not equally contributed during this time then you would be able to claim greater than 50% of the equity.
It is possible to claim greater than 50% of the equity in the property by litigating under the Trusts of Land and Appointment of Trustees Act if it can be shown that you intended to keep your finances separate and it would be inequitable for a 50% interest to be enforce, but this is a very specialised area of law and the legal fees are very expensive.
So, unless there is a declaration of trust your starting point for negotiation should be 50:50 or such other percentage as you think is proper and fair.
If there is a mortgage on the property then you won’t be able to transfer the property from your joint names to his sole name without either your partner remortgaging or otherwise repaying the current mortgage that you have.
He cannot transfer the property in to his name without you signing the land registry transfer, so do not agree to a price that you are not comfortable with.
My goal is to provide you with a good service. If you feel you have received anything less, please reply back. Please remember to leave positive feedback using the stars at the top of the page.