There are still lollipop ladies/men (crossing guards, if you will), here and there, but UK roads are nowhere near as dangerous as US roads: smaller cars, lower speeds, most of the roads between you and the school will be 20mph or 30mph limits, and so on.

I'd say even then, five is a little low by UK standards. I think I started walking solo to school when I was about 7 or so. By 11 I was walking a mile to a train station and catching the train 15 miles to another town (nearest Catholic secondary/high school). 5 years old is not far off 7 or 11, but it's a big chasm - be ready for it to go by in a flash! :)