Durgle valve in bedroom

[Murdo7]

My plumber wants to put a durgle valve in the new bedroom. Is this allowed and/or safe.
The bedroom is a new built extension that backs on to the existing bathroom. On the then outside wall there was an open vent for the soil from the toilet. Now he proposes to cap this with a durgle valve and box it in.

Any advise or regs that either allow this or don't would be helpfully.
I also worry that if the valve fails that a valve situated in a bedroom would create a situation where pathogens would be breathed in over 6 -8 hours without us noticing this.

Thanks

[welsh brickie]

better to extend it to the attic if possible