Sad to report that the Peregrine has Benn found dead in the river Tyne. The body has been recovered and will be examined though I suspect that the cause of death will be drowning. Though the nest box has been placed somewhere safe from interfering humans, perhaps it is just too risky a siting - the chick had only just been able to fly up from the ledge it was on to the box and then onto the top of the box and maybe it just tried to fly and couldn't get back to the box or either solid river bank. It may have chosen to land in the silt if the tide was out and just become bogged down, waterlogged and drowned there.
Sad news.
Lot to learn