James wrote after K wrote: (SNIP)

If the pruning was severe enough to cut beyond the green growth here and
there, then that region of the tree is unlikely to sprout any new growth
and will remain brown.


Thanks for the reply, it was probably the overcutting then. I actually
paid someone to do that too! Where the completely dead bit is, there is
one or too green leaves so maybe I will be lucky and some of it will
grow back or cover it.


It's because you left it too long before getting someone to tidy it up, once
at the proper height for a hedge (say 2 metres) you must start pruning and
cutting, just nipping out tips to start with, especially with a conifer for
the reason Kay mentioned.
A Leylandii hedge is very high maintenance as they grow so fast, needs
cutting twice a year minimum to look any good and keep it within bounds as
they never stop growing, in fact nobody knows how big they will grow
eventually as every one ever planted is still growing bigger.
--
Regards
Bob H
17mls W. of London.UK