Thanks for your question. I will try to help.
Generally, 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 so that there would be no doubt as to the percentage interests of each party at this stage.
I presume you did not execute a declaration of trust.
Therefore, the presumption works in your favour in that in the absence of an agreement now to contrary or litigation then you would be presumed to have a 50% interest in the equity in the property
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. However, contributing the entire deposit can form the basis of the claim though it is likely some or all of this might be offset during proceedings as a result of your mortgage contributions.
She would have to litigate to claim more than 50%. So, I would suggest that you see a local solicitor now and give your specific and detailed instructions to them with a view to negotiating a settlement which allows you to remortgage and pay her off on a 50:%50 basis or as near as you can get to it.
Finally – and this is important - 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.
I can tell you how to check how you hold the property if you wish.
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