Posted: 07/05/2017 at 19:21
I'd agree with KT but do ensure you know exactly where the boundary line is. The actual line can be as thin as a pencil mark on your Land Registry plans. It matters not who paid for what fence - the real key is that all important line.
If you think your neighbour's have overstepped the mark , then you can ask them to move the trees to their side of the line. I don't think that there is anything you can do to actually stop them from planting the conifers on their side but there is some sort of thing about "evergreen hedges and height". You may want to check this out if you think there is going to be a real problem. You are within your rights to cut off anything overhanging your garden but be aware that if you do that, you should not just dump the resultant branches into your neighbour's garden - you can offer them to your neighbour but if he/she declines to accept them, it's down to you to dispose of them yourself.
Your right to light is pretty "iffy" in your garden ( indeed it can be a bit iffy even if it affects your house ) so may be wise not to try that route if you can avoid it.
If this response sounds negative in the extreme, it is simply because I have an ongoing dispute with my neighbours and even involving solicitors and police hasn't resolved the matter. So, just a warning - tread carefully would be my recommendation.