Misdelivered medical letter

I just opened in error a letter addressed to the parent or guardian of “Baby Brave-boy” which has been sent to our address. Our surname isn’t Braveboy but we do have a young son and I mistakenly though this may have been a letter sent to us by a neighbour who doesn’t know our surname about our child!

In fact it’s the results of neonatal blood tests and the letter needs to be kept with the baby’s red book. We live in London with several GP’s surgeries in our catchment area and probably 300 residential addresses on our street so I have no way of tracing the actual parents of this child. A quick check on 192 doesn’t show anyone of this name living nearby. I could return to the hospital but as they clearly have the wrong address on file, I think it will just end up being sent back out to my address! What if anything would you do in these circumstances?