Just a quick note to say version 2 is out (auto upgrade), now major/minor gridlines and narrowed the minor lines. Much easier to see what is going on esp. when a large number of lines displayed. Hope people prefer the new version.

Edited to add (save replying to myself again

Just fixed a bug where gridlines where labeled wrong. Now if you are zoomed out too far you are just given a static rendering of the whole grid.

In fact you can download the static files here: Great Britain (inc 10k lines!) . Ireland (inc 10k lines!)