https://www.theargus.co.uk/news/23646867.age-child-can-stay-home-alone-uk-nspcc-advises/
Seems a bit old to me. I started leaving DS home for 1-2 hours age 9. He's now 10 and has walked to school by himself, gone to the local Sainsbury and the park. All within a 10 minute walk. He'll be 11 when he starts secondary school and I fully expect him to get the tube to school by himself (I'll train him of course).
12 seems a bit old to me. I know every child is different but surely this advice just makes parents with capable children feel like they are bad parents?