The legislation in relation to high hedges differs to other nuisances in that there is a requirement that those affected by the effects of a high hedge try to resolve the matter with their neighbour in the first instance. It is important to keep full records of your attempts to resolve the situation and the responses you receive from your neighbours.
If you are unable to resolve the matter you can make a complaint to the council but there may be a charge if the initial contact with the hedge owner doesn’t resolve the problem. Conwy CBC currently charge £320 for making a complaint.
http://www.planningportal.gov.uk/permission/commonprojects/highhedges/
https://www.gov.uk/government/collections/high-hedges