Updating post from Reddit.
(I’m in the UK) If a family member is signing to be my guarantor for a house rental through a letting agency, does the family member have to know about my credit history? Or do they just sign the same tenancy and my history is kept private? Thanks :)
On one hand, it isn't your guarantor/family member's information, so the landlord/agent shouldn't share it with them.
On the other hand, your credit records may be relevant as they may indicate the potential likelihood that your guarantor may be chased for your rent in the event that you don't pay your rent.
Be honest with your family about your finances. They should know what they're signing up for.
What have you said to the family member about needing a guarantor? Have you been open/honest about your finances not being in the best state of health - whether that be now or historically?
If you feel there may be further issues further down the line and they may need to pay your rent - then PLEASE PLEASE PLEASE come clean with them now - it is the decent thing to do.