I desperately need some advice.
I’ve got a builder to do a rear extension and he recommended a building regs consultant whom I went with.
It had been 4 months and the shell of the extension is up but I never saw the consultant and works sent i be crawling at snail’s pace so I called her consultant to ensure that everything is alright. That’s when he told me that he has never seen the site and wasn't told that works had started 
He then tells me that I need a build over agreement with Southern Water and I need to dig a new manhole in my garden as my extension will sit on top of a manhole.
Southern Water is now saying that they need detailed drawings of the foundation design, details of existing and proposed plans, including any known existing drainage arrangement.
My builder is not answering my calls now and I guess if anyone has these information, it is him.
Who can I ask to do these plans and drawings for me now? Architect, draughtsman or someone else?
Just the application alone to SW cost £1k. Can anyone who has done it before also advise how much the whole works is likely to cost me?
I am base in Gravesend, Kent