You can cut any branches that overhang your property, up to the boundary line. You must not cut anything on your neighbour's side. You must offer the cuttings back. They can say no, but you have to ask. Throwing them back over the fence is fly-tipping. Before you cut, check for nesting birds.
If the hedge blocks light to your windows, the council can intervene under High Hedges legislation, but this costs £300 to £500 and takes months. Talk to your neighbour first.
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