On Sep 22, 4:54 pm, AJH wrote:

Department of Trade and Industry
Management of Vegetation Near Overhead Power Lines
[snip] [...]

I'd found that after I posted here - but annoyingly it just gives the
extremes rather than some of the intervening figures.
My industry (forestry) quotes a "vicinity zone" but doesn't define it:

[figures snipped]

Thanks for that data - it is of some help.

MAT