Now the extension is complete I need to extend the existing MDPE pipe and bring it up through the kitchen to connect up. My thoughts are to deepen the trench around the perimeter to 750mm, connect the existing 20mm pipe via a quick fit to more 20mm pipe. All of which I have. 
Question is what is the best way to bring it up to the kitchen just under the window in picture. ?

This is the side view where the existing pipe is. 

4” plastic drain pipe for vertical with slow radius bend put join in an easy place to get to, I would not dig any deeper, next to it is deep enough already 

So how does the pipe work into the kitchen. Are you saying drill a big hole to fit it?

Sadly, once again, this is one of the jobs that should have been done right at the start when the foundations and first courses of blockwork were being laid.  Strictly speaking you bridge the gap over the water pipe with a lintel.  Yes i could not believe it when I saw my brickie laying a bit of lintel over a 3" gap be he said if BC see that bridged with just a block they will fail it.

 

Sorry written for the benefit of someone starting their project with apologies to @Chriswills  You have no option now but bash a hole through the wall from the inside to pass the water pipe through and cover it all up before BC see it.

No use to the OP but better method is bring the pipe through/under  the footing ducted in 110mm sewer pipe then carry the duct up to the finished floor.

It needs to be insulated ( rock wool down into the 110mm pipe will suffice ) plus pipe insulation over the pipe, if it’s less than 750mm ( iirc ) inboard from an outside wall. 

Do I need to fit ACO drains here or just add some gully pots for roof water and kitchen sink waste?