Had to look that one up, but thanks. Interesting. It's sort of what I've been thinking i.e if they've not made a formal complaint in 40 years then by default they must have accepted the situation
That MAY be the legal point
you may even be able to say "How do I know YOU didn;t plant it and it is your plant that has spread to MY garden
but for the sake of neighbour relations it may be best to take the view that it is a shared problem and "we" can sort it together
and if they start to mutter about legal stuff then you can say you think this is the case
mentioning that you have been to see a solicitor MIGHT be seen as aggressive
Best to be sure before you have to comment
(worked with my ex - she wanted loads of money every month when we split up and said she knew she was entitled to it - and gave this little smirk when she said she would get a solicitor to force me to if I didn't
in cash - of course
but she didn;t know I had already been to one and knew she was talking rubbish!
best to be pre aware and not mention it unless you need to)