Thanks for all your advice it is much appreciated, apparently they had the church tested five years ago, and alot of the wiring was condemned, so they have told me it will probably need rewiring, luckily they are not in a rush so i will have time to plan my test when i take a look, I am planning to visit some churches to get an idea of how others have been wired.
I have done more houses and factories than public/commercial installations. I am thinking pyro cable as this is what every church seems to have, but i am not sure on where and where not to drill holes through historic walls, but saying that i have seen some pritty bad cable installation in old walls.