It's ginnel around here too, but alleyway as well.
Think it depends on where the resident grew up. From WMidlands so alleyway to me & neighbour Southerner so she's the same, but PCSO uses ginnel. They arent allowed to work near to where they live, but she's still a northern lass.
OH's little house has one next to it, but for the life of me cant remember what they call it, def not ginnel nor alley/way.
Bjay, sympathies re drug situation for your daughter. We have had some past probs at the side/behind us, but touch wood, not for a few yrs now. Drinking teens, now that is the latest problem. J.