Garage conversion into a studio

[Johnsamjoe]

Hi, I would like to convert my garage into a studio and replace wooden double doors with a double glazed door with side windows. I have attached photos below. There is a manhole right in front of the gates. I have been searching but still unsure if this is a public or private sewerage. Most likely private because it is on the property. Here are the questions: Would I need permission from water company to replace the doors and build a permanent wall next to it? Or do I need to move the manhole for this project?

 

[motorbiking]

What is the proximity to the neighbour - is there any chance it connects? You could lift the lid and ask them to flush the loo to check.
Since your garage is already over the pipe, you could ask the water company to check if any Build over agreement was put in place or if its a private drain.