Hi, welcome to g o y, I think it highly unlikely it is dieing, just shedding a few needles, they will go brown on the inside because they don't regenerate from brown wood.
But look on the bright side, if it is dieing, you can get rid of it, and grow something a lot nicer, and a lot less bother, Derek.

I don't think that leylandii are necessarily bothersome Derek. If they are given the right care and attention then they can be a wonderful addition to a garden and serve a useful purpose. They have a bad name because a lot of people don't tend to them and just leave them to their own devises which causes problems, especially with their neighbours.

Thanks guys. I just walked past another this evening that was shedding a lot of needles but appeared ok - I just never noticed they did it quite so much at one part of the year.
I think neglect gives conifers a bad name, it's true - we're looking to reduce ours in height in fact. But there's a lot of wildlife that like it, plus it provides a lot of privacy.

They have their uses and make nice borders if kept under control. Keep it trimmed to a reasonable height and trim the sides 2 or 3 times a year. As you said, the wild life will benefit and it will look nice too.

I agree with Myron. We have a hedge that OH trims twice a year, it looks good and does a great privacy job.