Hi mike...

Thanks for replying!

Unfortunately I've got large areas of grass that are dominated by Yorkshire Fog; at a guess I'd say at least a quarter to a third of the lawn, in large patches. So it won't be practical for me to be so selective with the glyphosate. I think my choice is between nuking large areas and reseeding, or finding a long-term cultural regime that favours the fine grass at the expense of the Fog.

Something I didn't mention in my opening post was that I did glyphosate some of the very worst patches last year, where the Fog had formed particularly dense tufts. I then reseeded with fine grass. So I now have patches of very fine grass mixed in with the patches of very coarse grass, which admittedly looks a bit daft but at least it's a step in the right direction!