Hi Alicia and welcome to GoY. If they are brown they are almost certainly dead, you don't say where you live in the UK - was the ground waterlogged or very, dry? How did you look after the Cypressa after you planted them?

Dare I say they may have done you a favour? They do grow immensely tall and very quickly and unless you have a very large garden with no neighbour on the other side it can be a constant battle to keep them within bounds. There are much smaller cupressus that are better for most purposes. Sorry you have lost them though as its money down the drain.

Are the brown individuals brown all over or in patches? If it's patches I think there is Cypress Aphid to watch out for.