If the property is in your joint names, even if you have made little contribution to its purchase or the mortgage or maintenance, you will be entitled to a half share.
If you are not the legal or beneficial owner of the property, that is you are not mentioned on the deeds or the mortgage or in any trust document but have been promised a share of the property by your partner (especially if this is in writing) then you would be entitled to at least the amount your partner promised you providing there is evidence of this agreement.
If you have contributed to the purchase of the property or the mortgage or maintenance or there is evidence of a direct financial contribution you may have a claim especially if you have done something to your detriment, that is if you have acted in a way that has imposed a burden upon you, for example, carrying out major works at the property or paid substantial bills or mortgage payments.
If you are parents of children under the age of 18 who are living in the property, and there is no alternative accommodation and you have decided to separate, it may be that one parent and the child or children may be permitted to occupy the property until the children are adults. In these special circumstances the other parent could be excluded from his, or her, own property.
This can be a complex area of law, so please get in touch with the family law team for advice.