Whilst not wanting to sour the relationship between you and the neighbour is admirable, it seems that the neighbour does not share the same ethic.
The growth is trespass and you are entitled to remove the trespass and if you need to get someone in to do that, then you are also entitled to recover the cost.
As well as being trespass, because this is obviously going to be an ongoing and regular thing, you also have a claim against the neighbour in common law nuisance. You are entitled to take the neighbour to court (if he won’t do it voluntarily) for a court order to abate the nuisance which would basically be an injunction to make him do the work or enable you to do the work and make him pay for the cost.
You may find that a solicitors letter is going to have more effect than a word or letter from you and may avoid the need of going to court because he does go to court, I can not see how he can defend any action you bring.
.Can I clarify anything else for you?
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