It seems to be in an odd location with respect to the house, the flow would appear to be towards or under the house, is that an extension?
Also have you had the cover off to see if it is connected, it may just be an abandoned piece of pipe?
I really needs to be accessible, but looks like a nice new cove would be appropriate with new slabs.
Is the new level still going to be below the level of the house damproof course?
Looking at the angle of the top cover it appears to have been pushed down into the ground.
If you excavate around the pipe you may be able to bring it up to the new level then cut the slabs or whatever around it.