There is 'high hedge' legislation in place, which applies to evergreen trees and shrubs. However, this normally relates to hedges which form a boundary between two properties, whereas you state that these trees are on the other side of the boundary.
That legislation doesn't give you the right to demand that the trees are cut back. It simply allows you to apply to your local council for them to make a 'high hedge' order, requiring that the height of the trees is reduced. You have to pay a fee to the council to make such an application and they will only grant it if you can show that the height of the trees causes serious inconvenience to you
and that you've already attempted to resolve the dispute with your neighbour.
See here for further information:
http://www.direct.gov.uk/en/HomeAndCommunity/W hereYouLive/NoiseNuisanceAndLitter/DG_10029999
Chris