You can complain to the council if a high hedge is impacting on your enjoyment of your property, however, before proceeding down this route, you must have first tried to resolve it amicably with your neighbour, and taking it to the council should be a last resort.
There are places on the internet that says the max height of a hedge should be no more than 2m, but there is no max height, and the council will consider the location of the hedge before determining how much a high hedge should be reduced by - they may consider it reasonable that a hedge can still be over 2m.
Other factors are that the hedge has to be semi or permanent evergreen! There must be at least two shrubs or trees in a row, be at least 2m in height, it must form a barrier, to light or access, and it must adversily affect your enjoyment of your property by virtue of its height - however, If there is a problem caused by hedge roots, the council will not get involved.
If the council is satisfied you have done all you can to reslove amicably, and they agree that a hedge is preventing enjoyment of your property, they will issue a remedial notice to the hedge owner to require them to reduce the hedge height. Once the hedge is reduced, it must continue to be maintained at that height.