You are responsible and liable for your own tree, even if it is covered by a Tree Preservation Order (TPO).

If you're worried about the health and safety of a tree, you should contact a tree specialist, called an "arboriculturalist", who can give you expert advise.

Remember to check your arboriculturist is who they say they are, and that they have the right qualifications, as well as public liability insurance. You can use this list of tree surgeons.