I would do nothing but observe.
Because it happened to me -- only I wasn't the observer, I was the mum of the 7yo. He was left alone at a home briefly a handful of times before he was 8, and mostly walking to school alone for a few months when he was almost 8yo.
And it completely messed my head up after I was reported to NSPCC and SS called and advised me not to (but they didn't order me not to, iyswim). When I asked how old was okay to let my son do those things, SS couldn't possibly say. Keep in mind, they never met my son.
So now I live in an area where it is normal for eight to ten-yr olds to play out alone or go to the shops alone, but I have no idea if I will get reported to NSPCC if I let my son do the same. Someone has been completely two-faced, asking me nicely for details about my family, and then running off and reporting me to SS.
Sorry, did I mention that the experience has completely messed my head up? Undermined my confidence? Made me unsure about who is watching, who is a friend and who is really just out to judge me?
Oh -and teachers at the school knew that I was letting my son walk to school alone (well, technically he usually just went ahead of me by 5-10 minutes since I had another child to take up there), and they were okay about it. But it turns out that SS wasn't okay about it... nor was some nosy observer.
The worst part is that my mother was a social worker for at-risk children; that's another reason I'm so irate. I know the difference between managed risk and actual neglect.