A sewer in my patio

[neil75]

Hello
I was clearing some concrete and soil in the garden to make a patio and discovered a brickwork arch next to a loose manhole cover which looked very old. When I lifted the cover I discovered a subterranean chamber, which has now turned out to be the beginning of the public sewer, if I interpreted the map properly from the surveyor.
The problem is, its about 3 bricks higher than the bottom of the back door, and only 3m away from the house. How can I still lay a patio and even get outside, let alone worrying about bridging damp proof courses and stuff like that.
Another worry is access for maintenance - am i right in thinking the water people can come and get access to it whenever they need to? If I lay a patio do I just need to leave the manhole access? The brickwork looks in a bad way, like frost has got it, If i laid a patio would the brick arch support the weight above it?
Previously it was covered in a few different layers of soil, then quarry tiles, then slabs and concrete on top, like as though everyone before me thought it would be ok to just throw the new stuff on top of the old. It felt like a time team dig, except without the knitted jumpers.
Would a split level patio work?

[lutonlagerlout]

post a picture please
looks like you may need a raised patio though

cheers tony