www.gov.uk/how-to-resolve-neighbour-disputes/high-hedges-trees-and-boundaries
You can trim branches or roots that cross into your property from a neighbour’s property or a public road
You can only trim up to the property boundary. If you do more than this, your neighbour could take you to court for damaging their property.
If you live in a conservation area, or the trees in the hedge are protected by a ‘tree preservation order’, you might need your council’s permission to trim them.
Your neighbour is responsible for maintaining their hedges so they do not, for example, damage your property or grow too high. If they do damage your property, your neighbour may be liable.
rics-consumer-guide-boundary-disputes/Get an official copy of the title plan from HM Land Registry. This shows the general boundaries of your property. Bear in mind that the title plan is based on large-scale Ordnance Survey (OS) mapping and may not show small changes in the boundary, or even what type of physical feature defines the boundary on the ground. The red line on the title plan only indicates the general position of the boundary, and does not define its exact legal course.
Compare this title plan to your property. You should do this before exchanging contracts, you can ask the seller to clarify any differences, whether they relate to hedges and walls, outhouses or any other feature. Clarification of any differences is important as these may delay your exchange process.
Talk to your new neighbours at an early stage to identify the position of, and responsibility for maintaining, the boundaries.