Yup. The garage wall on the right is slap bang on the boundary of my property, and, as you say, the driveway doesn't quite reach the parallel edge. However, the whole lot was built like this in the early 70's (and hasn't been altered since), so I kind of assumed that the concrete edging on my driveway tarmac is my driveway boundary as such?
I'd say through experience your property ends with the extremity of the wall. The kerbstone is set to your side to denote you own it and it is your responsibility (in the same way fence posts denote it's owner).
You still own 4" of that grass.