manhole inspection chamber patio

Hi all, Thank you for reading this. I have applied for a build over agreement with Welsh Water and have just had a sewer trace performed. We propose to build near, but not over the public sewer at the rear of the property. As you can see from the attached plan that I've drawn post sewer trace...

I have started digging down to lay a patio, the plan was to fit a recessed cover around the manhole but I have noticed the top is higher than the patio level will be. The inside of the the inspection chamber is not brick so I am wondering if it is possible to lower or what other options I have?