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Well, now armed with Armillatox, we've had a go at the first stretch - here's hoping! Yes it does have a captivating aroma, but if it works I don't care.
Thanks to later respondents .. the sodium chlorate may be worth a try - I already have a big tubful (never tried it on moss, just weeds), so may have a parallel run to see which method works better.
Unfortunately, Pathclear does not give us a result on moss ... it has always been fine for weeds but the moss always hangs in (actually this year, even the grass and weeds have started to regrow whereas we normally only apply once per year - could be wet cold summer or could be the 'new' formula).
Thanks again for responses - will post a result here after passage of time in case that proves to be of help to others in the future.