Ahhh - suckers! That explains why I couldn't find anything when I
tried searching. Many thanks for the info.

The suckers are not very easily inaccessible which would make digging
back to the roots fairly challenging. Looking back at previous posts
the use of a topical weedkiller (eg glyphosate) has been suggested. If
I used something like this on the suckers - does anyone know what the
likely effect on the plum tree in next door's garden would be?

Thanks,

Michael