There is a disease called Box Blight that is caused by two different fungi. One is more serious than the other. Do any leaves have a dark staining at their base near the leaf stalk?

Mine go a bit brown from time to time on one side, I cut it out and they recover I have put it down to damage? perhaps by cats. But the whole bush brown maybe a different problem as Fractal says.

Are they turning brown or orange? There have been lots of questions about orange leaves on Buxus and the consensus of opinion seems to be cold weather.

Cold weather yet?

I've got my woolly jumper on!!

We have only had heating on for 3 days so far and its off again now still very mild here.

Fractal i haven't noticed any dark staining so am hoping it is just the temp change, in the summer months they all looked really healthy i also checked roots for rabbits nibbling at them as they have again started scouring for anything quite tender but i couldn't see any damage. Lets hope that they perk up in spring, thanks for all your help.