Foul and storm drainage connected

[daran]

I recently got some work done. The property came with a small area of patio and I got this extended. On digging up the ground I found the that the storm drainage had been connected to the foul drainage. The pipework is also above the level of the current patio level, thus when extending it's above the patio level.

Two key question-
1) Is it legal to connect the storm drainage to the foul drainage?
2) Should the pipework be below the level of the patio?

The pipework on the right the the foul drainage from kitchen waste and the right pipework is from the roof gutter.

Daran

[New Home Expert]

The question of is often depends on the water authority.  As a general rule it is not a good idea as a storm could and does put undue pressure on the foul drainage with any flooding having particularly nasty and unpleasant consequences.

Whether it is legal to connect the storm to the foul I don't know.
I have never come across this in new build construction until now.
The NHBC Standards state:

"Where the sewerage undertaker permits surface water drains to be connected to a foul water system: „„ an interceptor should be installed on the surface water side of the foul sewer junction, or „„ trapped gullies should be used."

Most drainage should be greater than 450mm below finished ground level. If it is any shallower, it should be protected with a concrete capping.

In your situation, I would look to connect the RWP outlet to the nearest storm drain run which should be below your proposed patio formation level.

More worrying, is the fact looking at the brickwork that originally, the airbrick was below ground level and I suspect your brickwork DPC is on the top of the airbrick? 
The dpc level must be 150mm above finished ground level.

[daran]

Thank you for the reply!

Unfortunately the people that I hired to the the job had to finish and thus the patio had to be put around the pipework (visually not nice!)
There is a 90 degree connection below the foul drain you see , which was cemented in, thus lowering was not an option without added cost. I did not want to spend my money to fix a problem that should have been done right the first place on a new build home.

I also am not sure where the nearest storm drain would be? As if it was under the patio extension region why wasn't the RWP connected to it in the first place? I would like to know if what they have done is legal/to standard- do I go via NHBC or council to get an answer to this?

What is the best way to resolve this?
What I don't want is for it to cause any problems in the future, rather have Persimmon fix the fault now!

In regards to the DPC being at least 150mm above ground- the patio was extended to the same level as the patio near the door. The garden area is uneven and slopes up away from house! The dirt mark you see was the level at which the grass was at, and the air brick was not covered, but the DPC would not be 150mm above grass/ patio level!

[daran]

Just measured DPC its 13cm from ground level, even at the patio which Persimmon put down in front of kitchen/ garden door (came with the house). To that level the rest of the patio was extended.

[New Home Expert]

The DPC at 130mm above finished ground level, whilst not perfect, would probably be OK.

I would ask the question of the drainage with your water authority. 
They will either condemn it, meaning you can then get/force Persimmon to put it right, meaning your patio would probably have to be taken up to do it, or confirm it is OK.