Hi Cosmicasca,
Thank you for posting about this to raise awareness of the issue. You’re right about how a redirection notification to the old address could be dangerous for someone fleeing abuse. Royal Mail ask that if there are personal safety concerns, people do not use the online form to set up their redirection and instead call customer services to set it up, informing them of the concerns, so that it can be done safely. The number for this is 03457 777 888, Monday to Friday 8am-6:30pm, Saturday 8am-3pm and Sunday 9am-2pm.
Take care and keep posting,
Lisa