Hi,
It does matter how the property is held. You do have to be married or in a civil partnership to use a Form17.
A Form 17 declaration however cannot be made where a husband and wife or civil partners own property as beneficial joint tenants. In these circumstances the couple do not own the property in shares at all but are entitled jointly to the whole of both the property and the income.
This is distinct from the situation where the husband and wife or civil partners own property as beneficial tenants in common where they are each entitled to specific shares in the property and the income arising. TSEM 9850 advises:
TSEM9850 - Property held jointly by married couples or civil partners: Form 17 rule - declaration must reflect reality.
Thank you.