I very much doubt if the microphone built into into your headphones is a reciever, only a transmitter.
A good microphone only costs a few pounds, or get a webcam to record sound and vision.
A word of warning.
To be Legal
Every person in that room must be aware that you are recording them.
(It is not good enough just to put them on a window ledge and hope everyone see's it, you must tell them physically)
The recording devices must in view
Any person in that room has the right to preview that recording.
It canot be made public without every person who is on that tape being aware of it.