I remember working for a firm, and we realised there were steam lines and electric cables going basic nowhere, and in some cases powering things no longer in use.
So we were tracing cables and steam pipes and finding where they went, and one seemed to go into a domestic properties back garden.
On approaching the owner, it seems her late husband was an engineer for the company, and the central heating was running from a steam line, and also all the electrics came from the factory. We have no idea if this had been sanctioned or not, but it could not continue that way, so she had to get central heating and an electric supply put in.
As to depth, I have seen a garden levelled, lifted etc, so when fitted the services may have been 1 meter down, but that is no longer the case. Sometimes one looks around, and one has an idea what it may be, but digging through a water or gas pipe is not what we want, and an 11 kV electric cable will go with a massive bang.
Should be tiles, or tape or something to tell you what it is, the last of summer wine ""Why Does Norman Clegg Buy Ladies' Elastic Stockings?" a comedy but so easy to drill through a water pipe.