Hi
You could do with posting this in the law section.
If you have contributed to the purchase price, or made contributions via mortgage payments.. or paying the other bills to allow the other person to pay the mortgage, then you may be able to claim an implied trust. This kind of trust is not evidenced in writing but is essentailly based on a common intention between the two people concerned.
However, in the absence of an implied trust there could be a case for proprietary estoppel, IF there were assurances that any contributions made by yourself would gain you a long term interest in the property.
Can you give more details?
Thanks
J