JOINT TENANTS
If you are both recorded on the Title Deeds as owning the property jointly and there is no mention of the ownership being in unequal shares (for example, you both put equal contributions into the property), it is assumed that you will own the property equally with your partner and will be entitled to 50% of the equity.
The Court will not look any further than the Title Deeds if it appears that the property is jointly owned as joint tenants and there are no further facts to consider. In these circumstances, it is unlikely to make an Order to provide either person with any more than 50%.
One of the main effects of owning a property as 'joint tenants' is that both yours and your partner's shares will automatically pass to the other from your estate should you predecease them.
If you are unsure about how you own your property you will need to check with the Land Registry.
TENANTS IN COMMON
There is a second way that a couple can own a property and that is as 'tenants in common'.
This situation is likely to occur when one person put a higher contribution into the purchase of the property and it is recorded by a Deed of Trusts. If you then split up, your legal entitlement will be as recorded in that Deed. If the Deed does not actually specify an unequal share, the Court will assume a 50% interest.
One of the main effects of owning a property as 'tenants in common' is that your share in the property will pass in accordance with your Will or in accordance with intestacy law if you have not made a Will. It will not automatically pass to your partner.
It is possible to change from owning a property as 'joint tenants' to 'tenants in common' upon separation to ensure that your interest can pass to whomever you choose by severing the Joint Tenancy.