I found it!
Whilst the Hubster was filling the hole in the front yard, I took a 3ft metal spike and tested the ground around two external faucets. I am not strong and at the second one on the north side, I was able to easily push all 3ft into the ground. And when I removed it there was definite damp earth attached. So I showed the Hubster the evidence, he started digging and very soon the proof we had been looking for appeared. A foot down we hit WATER! The further he got down the worse the water, but finding the pipe took some time and digging. Finally we found the culprit, the collar had cracked between the 1-inch PVC and a galvanised pipe (Hubster dictated this techy bit!). And it was spewing out all over the bloody place with force! This was only about 10 seconds worth of water, before the main was closed! We don't use this tap at all, so the decision was made to cap it off. A piece of PVC pipe was removed, the capped end fitted and a block of wood placed between to exert pressure to stop it blowing back off.There really wasn't much I could do to help with this repair and so I was delighted to at least be able to find the problem for him. He finished up, whilst I cooked him a special dinner as reward for all his hard work.Good to know we won't be bankrupted by a water leak!