conifer hedge

It can be lack of water, sun scorch (unlikely in UK), or possibly wind burn. I think it's normal to get a few brown bits at the end of winter or if the tree has been damaged in some way. Extensive brown is not a good sign. We live in a hotter climate than UK and take care to water well in the summer. We've found that heat or drought does more damage than the cold winters.

It could also be that you cut those sections too hard back when trimming your hedge. If you did, unfortunately, the conifer won't send out new shoots from dead internal wood.

I think it could be wind burn, but as much as i love my cat.If a cat decides to spray against them that makes them go brown, i have a conifer hedge & my cat smokey is always doing it, the hedges are still ok, but where he sprays they are brown round the bottom.