click on the little tree icon to add a photo.
if you scratch the bark with your thumbnail and it's green underneath , it's alive, if brown, it's a gonner.
patience is needed here Gavin.
Spray with liquid seaweed,it might help.
What sort of size are they Gavin and in what size of pot? Anything in a pot needs a bit of extra care re feeding and watering. Wind can dry potted plants out just as much sun too. It may simply be that one is catching more sun/wind than the other
At this stage feeding isn't really a priority Gavin. I think you need to determine what's causing the issue first. In my experience, box going brown is either short of water or has caught too much wind or sun.
Make sure they're not sitting in water either - if you put your finger into the soil/compost it should be damp not soaking wet. If the soil's very wet you might need to check that the drainage holes aren't blocked. If it's dry lower down than about an inch, they need more water. Most plants in pots need watering every day or every other day during summer. Rain doesn't penetrate through evergreen foliage either - even if it's raining quite heavily for long periods. If the pots are in the shelter of a house wall, they'll be drier than ones out in the open too.
Without seeing them it's difficult to offer any other suggestions at the moment. Someone else here may have some further thoughts though