There is no obligation upon an owner to maintain a hedge to a particular standard. There are some points of note however:

There may be a restrictive covenant requiring the maintenance of a hedge. Details of such a covenant would be found within the Title Register and Title Deeds

If the hedge trespasses or causes a nuisance or injury then there are actions available. You should seek the advice of a barrister in such an instance.

Relevant documents:

Title Register

Title Plan

Title Deeds

See Also:

What is a Restrictive Covenant

Hedge Ownership

Hedge Planting