A couple may reach an understanding about what will happen to their property if they separate. They may have relied on this understanding during a long relationship and structured their affairs in particular ways.
If, however, they have not made the agreement by following the correct procedure, the agreement will have no legal effect.
Sometimes a partner can ask the court to order that the agreement is to apply even if it was not made in the correct way. But to make these orders, the court must be sure it will not affect the other partner unfairly. The court rarely uses this power.