un-vented drainage dilema

[gormless norm]

Hello there,
i'm seeking some level headed advice regarding the drainage for my understairs toilet.
Due to an abhorrence on the part of my plumber,i find myself with a soil pipe entering my understairs cupboard in readiness for a w.c and basin,which feeds into the drains at a distance of approx 7 metres.[The abhorrence being that there is no open vent on this run.]
Now it is not feasible to vent this pipe to the outside in any way,as all the pipework is buried under 3 months of very hard work!.
(new extension) My question is, if I build a stub stack with durgo and fit my toilet and w.c as planned, will my house really be blown to bits along with the rest of the terrace?
I know this is outside of building regs,but i don't want to forsake my downstairs toilet if i don't have too.
What is the probability factor of aforementioned holocaust?

 

[ChrisR]

WHat's the fall?

 

[gormless norm]

The fall on this pipe is about 30mm over a metre.

 

[gormless norm]

I forgot to mention that the pipe in question and my soil stack share the same ic

 

[bab]

as far as i'm aware what u intend is fine. compliant with regs as wel, if the drain connects to the same i/c as an existing soil/vent stack. cool. the stubstack is perfect, a lot dont even bother with that, fit the basin with an anti-vac trap as well. a w/c may have a 110mm pipe but it only flush's 1 3/4" so a horizontal pipes not gona give ya much grief.