Unfortunately, UK schools have gone ridiculous in curbing kids' indepedence skills.
To do with their insurances i think and fear of liability if a child comes to grief on the trip.
I have 5 kids.
Child 1 born 1993, child 2 born 1996 both walked 15 mins to school from 5½ years and no one batted an eye.
Child 3 has learning disabilities and had to be driven to a different school.
Child 4 i had to get permission from the local authority (he was born 2002) as it is now a 'grey area' as to who takes responsibility if he doesn't make it.
They do agree to let him walk but he was nearer 6.
By the time child 5 is born (2007) even I am beginning to question my own parenting as by now everyone drives their child to school (this is the 15 min walk school) and only really very few 10 and 11 yr olds walk.
So I had her meet me at the path next to the school from 6 yrs but she didn't walk home til about 8yrs and even after that i used to meet her at the school path quite often after school.
And, since covid, the same school has gone ridiculously over protective.
Children up to 8yrs old have to be met at the classroom door by an adult (over 16yrs) and the teacher hands each individual child to the adult.
They cannot even cross the playground alone.
The danger at the school compared to 25 yrs ago is the amount of parents' cars parked all around the school. There have been no abductions or any change to the routes to school apart from selfish parkers.
So, OP, I totally agree with you that you know your kids and that kids that kids that are on target with development and have plenty of pre school experience of walking with an adult, learning how to cross safely and stick to the route, use the pavement etc, should be perfectly capable of going it alone.
But, unfortunately, in the UK, you are probably going to be in a small minority of one - and unfortunately that means that your kids won't be walking to school with their pals. I'm with you on this though - they are old enough if they are up to speed with development.