Check of Drains layout - Can you join a vertical vent pipe underground?

[BobSlayer]

Hello there

Can anyone see any problems with the drains plan below?
(it is amended and updated from an earlier question)

The question we aren't sure about re Building regs:
Can the branch from the toilet join the vertical soil vent pipe? This join would be under the floor.

"O" in Utility = Soil Vent Pipe with rodding access
"O" in Toilet = Stub stack with rodding access
"S" in toilet is shower branch

- Ground floor (of 2 story cottage)
- The Kitchen and utility are a new extension
- The Bedroom and Toilet are a converted garage
- The dotted lines represent new drains (private)

Big thank you in advance

 

[BobSlayer]

The alternative (below) would be to join the pipe down flow of the vent pipe in the utility - this was the solution suggested previously in this forum by Woody.
However as you can see this will necessitate the vent pipe being in a different corner of the Utility
- which is proving difficult to make work for the existing upstairs WC

Hence why the question - can a branch drain join into a vertical vent pipe?

Alternative: