Tenants in common each own a distinct share of the property, and can bequeath their share to someone else in their Will. They are presumed to have equal shares, unless there is evidence to the contrary. Tenants in common can choose to have unequal shares, for example to reflect the amount each contributed to the purchase price.
So if we’re tenants in common and I have the greater share, how can I protect my interest?
You need to ask a lawyer to draw up a legally enforceable document, called a Declaration of Trust, recording your respective shares and also how any increase or decrease in the value of the property is to be apportioned. Without this, you are presumed to own the property in equal shares. In some cases, you can challenge this presumption in court but it is a difficult, expensive process with no guarantee of success.
If our relationship breaks down, is my interest in the property protected?
It depends on your circumstances, including whether you are married/in a civil partnership or cohabiting. If there is, unfortunately, no future for your relationship, and if you own a property as joint tenants, it is usually advisable to switch straight away to tenants in common. All you need to do is give your former partner notice in writing that you are severing the joint tenancy. There’s no requirement for them to agree, or even acknowledge the notice. You will then own a distinct half share of the property (subject to mortgage, if any). If you died, your half share would pass under your Will or the intestacy rules (if you had no Will). It would not automatically go to your former partner. This gives you some protection in the interval between the relationship breaking down and you entering a separation agreement or finalising your divorce/dissolution of civil partnership.
In the longer term, do I get to keep my share in the property (or its sale proceeds)?
If one of you applies for a financial settlement in the context of divorce/dissolution of civil partnership proceedings, potentially all of your assets are put into the “pot” to be divided between you. The court has a number of options for dealing with properties, including the family home e.g. transfer it into the name of one party; sell it now and divide the proceeds as the court sees fit; allow one party to live in it e.g. as a family home for them and the children until the youngest finishes school, then sell it and divide the proceeds between you. The outcome depends on all the circumstances of your case, including which other assets and how much income each of you has.
If you are not married or in a civil partnership, it depends on whether you and your former partner entered into a Cohabitation Agreement, recording what happens if your relationship breaks down and what each of you is entitled to. This should include provision for any properties you own. If there is no Cohabitation Agreement, in the eyes of the law neither of you has any financial obligation towards the other. One of you can buy the other out (subject to your mortgage company’s consent), or the property can be sold and the net sale proceeds divided between you. Unless you have a Declaration of Trust stating otherwise, it will be presumed that each of you is entitled to half.