A quick update - this problem is now solved and is I suspect rather unusual.
I have monitored the incoming water pressure using a home assembled logging device based on an Arduino microcontroller together with a 0-100psi pressure transducer purchased from Amazon.
Having logged the pressure...
We are at the end of a fairly large extension project which included the installation of a new water main. This is a largish old property which is supplied in different parts by two branches of rising main both of which are supplied by a common supply meter. The new extension is fed by one of...