Current in Dead Circuit

[Mr_cellophane]

I have disconnected a power shower pump and boiler and want to disconnect the cable from the main fuse box.
I identified the breaker as turning it off turned off the neon light. There were three cables on the breaker, the downstairs ring and the boiler/shower. I removed one and connected the live and neutral together (I had turned the main switch off). I then went up and checked for a circuit from the shower switch. I then checked for a circuit from the boiler switch. Both beeped showing that I had the correct cable. I then disconnected the live and neutral and checked again - no beep. I was then 99% confident that I had the correct cable. I then turned the power back on and checked both switches for a current.
I did one final test, which is where my question comes. I connected the live cable to an earth bonded copper pipe and got a reading of 40 volts. Where does this come from. If it had been 240v, I would have been very worried, but why only 40 ?

 

[breezer]

induction

 

[bengasman]

One fuse or breaker should have only one wire coming out, it could well be that there has been some untested adding to the system. If you can measure a voltage on the cpc, your bonding is bound to be faulty. You may find getting a proper periodic inspection done a good investment. The last time I found a significant induction voltage, the house was literally lethally dangerous. Not saying your house is, but there is definitely something wrong, could be minor, could be major.