Firstly for sure it depends on the child – will they be sensible and how do they feel about it?
My DC all walked home after school and let themselves in from year 5 which is 9yo/turning 10.
Before that they were left for 10-15 minutes while I walked a sibling to Beavers etc – the left child would be 8/9 and more than happy to watch TV rather than trek up the road.
I think it needs to be done in gentle stages towards independence. Walking home from school, with friends, other families, is IMO a very safe way to start the process.
Overall I think a 9yo is fine to be home for an hour as long as they are happy with it and can contact you if they need to.
I'm surprised someone has suggested 8 years old. That's far too young and if a police officer knocked on your door to find an 8 year old on their own, you may find yourself locked up for child neglect and a referral to social services.
Highly unlikely tbh thank goodness. "Far too young"? What age is OK then? My DC knew the right thing to do in an emergency at age 8. @Naffatthinkingofnicknames you must know that leaving an 8yo child alone is not illegal? What is illegal is neglect. I don't think the examples given here are neglect.
And the shock about schools allowing them to leave alone – schools vary and plenty of junior schools allow DC to leave on their own.
I'm more shocked that a PP says they are not happy to leave a 13yo for an hour tbh.