Many thanks for all the replies, Its very strange and seems to be steel rather than cast iron as i accidently hit it with a pick axe and a cast iron pipe would have shattered.
The house is between 35 and 40 years old and all the drains etc are pvc.
Reason i have been digging holes in the garden, there was a drainage issue in that part of that side garden always became a quickmire after a few days heavy rain, there was no where to run a french drain to and found out that there was only a few inches of soil in most of the garden and after that hard compacted stones and clay.
Have been digging out trailer loads of clay and stones and replacing them with compost, grass and hedge cuttings.logs and woodchips/mulsh the drainage seems to be cured now but thought i would just dig another hole and bury some more logs.
Some more pictures but think the pipe or what ever it is must have been there at least 35 years really can not see any useful purpose for it and have no idea what it could be?
Grass etc is a bit of a mess but my intention is to rotovated a lot of wood chips into the first few inches and reseed early next year
Lol HMS Dave and roadrash tbh if its a big ring then it would a really big job and even if i started there would always be the risk its there for some reason? Knowing my luck i would break it and find water or some thing else Gas maybe shooting 50 feet toward the sky?