A tree which has become diseased or unstable will require removal before it becomes a hazard both to personal safety and property. Hiring a professional tree surgeon will ensure that the project is undertaken in a safe and responsible manner with all considerations in mind.
Usally Under common law
You may prune unprotected trees or hedges overhanging your land without the consent of the owner but you must
not trespass on to your neighbour's land to do this. In addition you must offer to return the timber and any fruit attached or which has fallen on to your land.
It is also considered neighbourly to notify your neighbour of your intentions prior to carrying out the works.
The above may also be applied to root encroachment.