[EF80TVVALVE]

Thanks for the replies both, I found it unusual to have the coil in the bell box too as I can't find any photos similar online. I have attached a picture of the internals of the main phone unit. Currently it is stripped somewhat but all that is missing is the dial mechanism and the four wires which go to the bell box. There is also no sign of any coil being previously fitted into the main phone unit.

Also the wires to the bell box are actually fed through holes drilled in the top of the bell house casing so there are no wires connecting the phone and bell box externally and the handset cable goes to the bell box directly leaving the hole at the rear of the pyramid casting free from any cables.

The coil in the bell box looks to be an original fitment too, it's all too neat for this to be done by someone by the looks of things.