I've traced the pipe run by injecting a signal into the pipework and tracing with a small pocket size short wave receiver. Easy access, under liftable floor boards, to the pipe run in the middle of the house, with pavement stopcock open I can hear a leak via a piece of broom handle and with company stop c*ck off there is no leak hiss noise. With kitchen isolator off and pavement one on there is a hiss. No obvious damp in that area of the house. Assuming I successfully freeze the pipe and water in the middle I can then determine which side of that mid point. One end is in garden soil and the other under concrete of the kitchen floor , under there somewhere is a conversion from lead pipe to copper pipe, likely problem point ?.
Any ideas?. Would a microphone and silicon grease to the concrete floor or metal plate rammed in the soil pick up enough sound when put through an amplifier be able to zero in ?