Hi ,
 
Thank you for your question.

As the property is held jointly between you and your parent it is your decision on how your split the income i.e. 50/50, 20/80 etc. each share would then have to be reported to HMRC in the usual way.

A declaration of beneficial of interest in a property (Form 17) is only to be used by married couples or those in a civil partnership who hold a property jointly.

Thank you .