Drainage runs for extension

[matlob]

Hi,
Looking to start an extension and need to get started as pp is expiring soon

Am I able to do the following drainage runs under a new extension. Will also be placing a WC in what is currently the garage

Some rain water currently runs into the sewage drains which I thought was a no no but this is how it was originally set up

I'm going to start digging trenches for the footings and get the drainage runs/pipework in so it can be marked as started. Am I right in thinking that any drains need to be 500mm from the foundation trenches.

I had drawings done a few years ago but they were very light on the details and the company is no longer there.

I will get BC out for the initial consultation but want an understanding first, so any help appreciated.

EXISTING LAYOUT

EXTENSION LAYOUT

 

[noseall]

If the blue lines are a separate storm system, I don't understand why the downpipe to the right of the main house, is not going into the same system. Unless you are on clay, any new storm drains are preferred to go into a soakaway on your own property.