is there a limit to the hieght of a conifer tree?

If its leylandii, then it will keep growing and never really stop! I have seen enormous ones, beyond any normal tree height still growing.
There is i believe a hedge law recently come in but not sure if it related to leylandii or hedges in general. I think they cant be allowed to grow over 6 foot, and some have to be lowered. Although chopping one in half or chopping more off it tends to kill them, what a shame! Speak to your local council to see what their legislation is on hedge height. I dont think they will concider the fact that they cause Sky to go off a problem!

If its actaully rubbing the dish and is overhanging your boundary then you are within your rights to cut it off back the boundary line, and legally return the cut pieces as they do belong the that neighbour

Maybe your neighbour would trim it down if they knew it troubled you, or you could go halfs and get someone to do it for you, It's worth a try!!

Depending on the species of conifer, they can grow from 1 metre tall when fully grown to 100+ metres tall when fully grown.
From your question I'm asuming the conifer is a single tree and not a hedge.
If the tree was large and established when you moved into the house -tough, you knew it was there when you moved in.
If it has grown that tall since you moved in, ask your neighbour if he can have the tree prunned. He will need to check with the local tree authority (council) first BEFORE starting any work as the tree might have a Tree Preservation Order on it, making it illegal to cut down or prune it without their permission.
As Nickyt08 has previously said, If the tree is overhanging your boundary then you are within your rights to cut it off back the boundary line, and legally return the cut pieces as they do belong the that neighbour. However, it's always best for neighbourly relations to ask first. Check for TPO with Council BEFORE work. Or you could reposition your sky dish.
Sorry if the third paragraph seems harsh, but that's the way it is without the fancy waffle. ;-)