The relevant legislation only applies to evergreen hedges. (i.e. it doesn't cover individual trees and it doesn't cover deciduous hedges). But it does give you the right to involve your local council if there's no other way to get the height of the Leylandii reduced. You have to pay a fee to seek a council order to get the hedge cut back. (There's no automatic right to such an order; the council consider each case upon its merits). See here for further information:
http://tinyurl.com/owzcu3
Chris