I have a Leylandii hedge (which I'm fairly content with, thanks Just
past it is what I assume is a spare tree that was left when the hedge was
planted. It has that same lemony (?) smell. It's pretty thick and shaggy
looking and currently stands at about 18'.

I have nothing in particular against it, the local birdlife loves it. But
I'm sure it's grown about 3' just in the one year we've been living here.
As the garden's only 20 feet or so wide, I guess it could soon be a problem.

Does it sound like Leylandii? Would I be wise to terminate it? Is there a
best time to do this so as to least disturb the blackbirds etc. that are so
fond of it?

thanks,
G.A.