I decided earlier this week to investigate further the drain hose we found down the garden, and came up with the problem.
Some idiot had decided that by just stuffing a hose into the tube from the Grease Trap, which takes all the grey water from the house, and not even sealing the joint would be sufficient.
When I dug the hole, I thought at first I had damaged the pipe, as the hole filled with water so fast, but as a I dug a trench to allow it to escape, the problem soon surfaced as you can see.
I have spoken with Jaime, and this is now another project, we will have to break open the Grease trap, which should have an access to clean it, but doesn't, connect all the pipes, and move the grease trap down the garden, amongst the trees, the water can then be released there. The old grease trap will then be filled to avoid any smells in the future.