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Thanks for your question. You can cut overhanging branches away yourself. However if the light is still being blocked and you have asked your neighbour to do something about it, without success, then you can ask the local authority to intervene and apply for a high hedges order. That order would force your neighbour to take action and remove those parts of the trees causing a lack of light. I'll post the rules for which are on the Scottish Government website.
Here is the link: http://www.gov.scot/Resource/0044/00445025.pdf