Sorry for the delay in replying. At present they are connected to the metal case of the fusebox, to its earthing point and is using the armour of the old 2 core 2.5mm SWA. There is T&E cabling running along some of the frame to the lights, but the earth system seems to work ok as I had one cable pull out of a junction box and touch the frame (clearing out old timber) which tripped the RCD in the house instantly.
The bonds will be connected direct to the new consumer unit as and when I fit it as the old box will be going. But if 4mm isn't enough, I could go up to 6mm.
All the old cabling will be going as well and being replaced with conduit. Actually, everything old is going and will be replaced as this is very much a project.
Thanks, but I was aware of that.