"

I would not regard a row of Leylandi type trees as a hedge.

It certainly is considered so within the 'high hedges' legislation (but
that doesn't apply AFAIK here, as the OP is in Scotland)
--

When does a group of trees become a hedge? Even if they are clearly set
back from the boundary and maybe mixed species, they will still have the
same light blocking effect. If you have a copse, orchard or arboretum could
the same restrictions apply?