Many thanks Lyn L, not a silly answer at all, could possibly be the solution. They do extend the full length of the space. Why copper?
Most of the other metal work there is composed of material that does not have the possibility of causing a spark. Not sure English Heritage would add anything to the building without good reason, they do tend to be very protective of keeping the fabric as correct as possible.
I did ask the property stewards and they did not know why.
Thanks for your thoughts.