Here is the map showing areas that are still lacking any butterflies records at all. I've roughly overlaid it with the 10km grid squares for convenience. It's worth remembering that the many of the areas surrounding these squares aren't really much better recorded (often containing no recent records).
Since I first made a similar map several years ago, well over 50 of these tetrads (2km x 2km grid squares) have been filled in. If you spot a square close to you, why not plan a visit or two this summer and note down which butterflies (and moths!) you see!*
* (of course doing so using public footpaths or getting landowner's permission)