There is no legal minimum distance. You need to think about the spread of the tree as it grows towards the neighbour's boundary. You probably need 50-60cm gap. The neighbour will be entitled to trim any foliage that grow across the boundary. Contrary to advice given on the other posting of the same question, these trees don't have large root systems and the probability of them causing subsidence issues is zilch. I grubbed up one of 70cm trunk diamter using a 2-tonne digger, but couldn't remove a smaller oak tree root.
But as others have said, these trees are a menace if not trimmed twice a year - and that's a lot of trimming. Why not find a slower growing more-attractive conifer.