Posted: 13/05/2013 at 18:11
It's going to be quite difficult to find anything very narrow if you want it to be so high - many hedges if that high need enough width to balance the height or they will be vulnerable to wind damage- you will also have a wait until you get the height you need. You could plant some trees with light canopies so they don;t cast too much shade but this might not give you the level of privacy you want? (Rowan and silver birch.almelanchier lamarckii are fairly light).
You can trim back conifers but musn't cut further back down the green growth as it can't re-generate - am guessing that this isnt given you enough of a 'reduction'.
The narrowest option would be to use trellis and cover this with evergreen climbers - mixing a couple would also give you a mix of foliage and flowers in your garden - but there are council planning limits on the maxiumum height for boundary fences which you would need to check. But a combination of this with maybe a strategically placed light canopied tree may give you the level of privacy that you want. Breaking up your neighbours view of you and yours of them can be just as effective that a solid barrier. If you place the tree away from the fence it will create a greater sense of privacy for you than if placed on the boundary - try it out in various positions until when you stand back it blocks your view of their window(s)
Hope thats of some help